65FR38373 Accuracy and Coverage Evaluation; Statement on the Feasibility of Using Statistical Methods To Improve the Accuracy of Census 2000, Part 1/4
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[Federal Register: June 20, 2000 (Volume 65, Number 119)]
[Notices]
[Page 38373-38398]
From the Federal Register Online via GPO Access [wais.access.gpo.gov]
[DOCID:fr20jn00-120]
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Part V
Department of Commerce
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Bureau of the Census
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Accuracy and Coverage Evaluation; Statement of the Feasibility of Using
Statistical Methods To Improve the Accuracy of the Census 2000; Notice
[[Page 38374]]
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DEPARTMENT OF COMMERCE
Bureau of the Census
Accuracy and Coverage Evaluation; Statement on the Feasibility of
Using Statistical Methods To Improve the Accuracy of Census 2000
AGENCY: Bureau of the Census, Department of Commerce.
ACTION: Notice.
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SUMMARY: The Director of the Census has issued Accuracy and Coverage
Evaluation; Statement on the Feasibility of Using Statistical Methods
to Improve the Accuracy of Census 2000, his statement on the
feasibility of using modern statistical methods to correct Census 2000
counts. The document sets forth the rationale for the Census Bureau's
preliminary determination that (1) statistically corrected census data
can be produced within the time frame required by law and (2) that
statistically corrected data will be more accurate. The Secretary has
adopted the Director's analysis and conclusions in a written decision
forwarded to the Director. For public information, set forth below is
Accuracy and Coverage Evaluation; Statement on the Feasibility of Using
Statistical Methods to Improve the Accuracy of Census 2000, as well as
three related memoranda (the Director's memorandum transmitting the
document to the Secretary, the Secretary's memorandum to the Director,
and a supporting legal opinion of the Commerce Department's General
Counsel).
Authority: 13 U.S.C. 141, 13 U.S.C. 195.
William G. Barron,
Deputy Director.
June 12, 2000.
MEMORANDUM FOR The Honorable William Daley, Secretary of Commerce
Through: Robert Shapiro, Under Secretary for Economic Affairs
From: Kenneth Prewitt, Director
Subject: Accuracy and Coverage Evaluation: Statement on the Feasibility
of Using Statistical Methods to Improve the Accuracy of Census 2000
Attached is my statement on the feasibility of using modern
statistical methods to correct Census 2000 counts as stipulated by the
U.S. Supreme Court's decision in Department of Commerce v. United
States House of Representatives (January 1999). This statement was
prepared after extensive discussions with the U.S. Census Bureau's
senior staff and review of all relevant documents.
The Census Bureau is committed to making its data as accurate as
possible for all uses. This document sets forth the rationale for the
Census Bureau's preliminary determination that (1) statistically
corrected census data can be produced within the time frame required by
law and (2) that statistically corrected data will be more accurate.
ACCURACY AND COVERAGE EVALUATION
STATEMENT ON THE FEASIBILITY OF USING STATISTICAL METHODS TO IMPROVE
THE ACCURACY OF CENSUS 2000
Table of Contents
Executive Summary
Background and Overview
Uses of Decennial Census Data
The Differential Undercount
Summary of Census 2000 Operations
The Accuracy and Coverage Evaluation Methodology
The A.C.E. in Brief
The Sample Design
Conducting the Survey
Dual System Estimation
Assessment of Feasibility
The Definition of Feasibility
Operational Feasibility
Release of Data Products for Use in Redistricting
Operational Considerations
Resource Considerations
The Census 2000 Dress Rehearsal
Technical Feasibility
Defining Numeric and Distributive Accuracy
Importance of and Relationship Between the Two Types of Accuracy
Impact of the A.C.E. on Accuracy
Historical Experience with Coverage Measurement Surveys
Demonstrates Feasibility
The 1980 Census Experience
Early Research and Development for the 1990 Census
Litigation Challenging Decision to Halt 1990 Adjustment-Related
Planning Activities
Conducting the 1990 Census and Deciding Against Adjustment
Postcensal Estimates and Survey Controls Decision
Early Census 2000 Planning
The Census 2000 Dress Rehearsal
External Review
A.C.E. Implementation Issues
Measuring Accuracy
Assessment of Issues Emerging from 1990
The Proper Standard to Use in Deciding Whether to Statistically
Correct the Counts for Non-Apportionment Purposes
Numeric v. Distributive Accuracy
Correlation Bias
Accuracy at Different Geographic Levels
Consistency with Demographic Analysis
Timing
Level of Sampling Variance/Smoothing
Level of Nonsampling Error/Bias
Enhancements to the Matching Process
Enhancements to Computer Processing
Enhancements to Minimize Missing Data
Homogeneity and the Synthetic Assumption
Additional Design Changes from 1990
Use of the Telephone in A.C.E. Interviewing
New Treatment to Account for Movers
Search Area for Matching
Reporting More Than One Race
Making the Final Decision
Conclusions
Bibliography
Executive Summary
This document sets forth the rationale for the Census Bureau's
preliminary determination that (1) it is feasible to produce
statistically corrected census data within the time frame required by
law and (2) the statistically corrected data will be more accurate.
Data from the decennial census are used to produce the state
population totals for congressional apportionment. Additionally,
detailed state data are used for redistricting, federal funds
distribution, and other public and private sector purposes. Section
141(b) of Title 13 requires the Secretary of Commerce to report state
population totals from Census 2000 to the President by January 1, 2001.
Section 141(c) requires the Census Bureau to report redistricting data
directly to the states by April 1, 2001.
The Census Bureau is committed to making its data as accurate as
possible for all uses. In accordance with a 1999 Supreme Court ruling,
the Census Bureau will not use statistical sampling to produce the
state population totals used for congressional apportionment. Because
the Census Bureau expects it can produce more accurate data by
supplementing traditional enumeration procedures with statistical
sampling, it plans to use these statistical methods to produce the more
detailed data required for redistricting and federal program purposes.
Prior to April 1, 2001, the Census Bureau will have completed an
enumeration of the American population, including a coverage
measurement survey, that is designed to improve the accuracy of the
initial counts. The coverage measurement survey, called the Accuracy
and Coverage Evaluation (A.C.E.), is based on the established
statistical method known as Dual System Estimation (DSE) and is
designed to correct for missed individuals or erroneous enumerations in
the traditional enumeration. The method of Demographic Analysis will
also be used to evaluate the completeness of population coverage in
Census 2000 at the national level, and to assess changes from previous
censuses.
[[Page 38375]]
The operations used to produce the apportionment counts are
designed with the goal of counting and correctly locating every
individual residing in the United States on April 1, 2000, and also to
count federal employees and their dependents living overseas as of that
date. This goal cannot be completely and accurately realized. Every
decennial census, from 1790 to 1990, has included in the census counts
some who should have been excluded, and has missed some who should have
been included. The first source of error leads to an overcount; the
second source to an undercount. Every census for which the effect of
these errors has been systematically measured has shown a net
undercount--that is, the number of residents who were missed was
greater than the number of erroneous enumerations.
Furthermore, in studies going back to 1940, the Census Bureau has
documented and measured not only an overall net undercount, but also a
higher net differential undercount for the Black population than for
the non-Black population. Studies from the 1990 census also indicate
differentially higher net undercounts for the Hispanic population and
American Indians on reservations, compared to the White population.
This persistent problem of differential undercounts is the most
significant error for the population totals obtained through the
traditional enumeration. As part of the operations for Census 2000, the
Census Bureau will conduct the A.C.E., which is designed to improve
census accuracy by increasing overall coverage and reducing the
differential undercount. The A.C.E. also corrects for the smaller,
though not insignificant, overcount that occurs when erroneous
enumerations are included in the census.
The Census Bureau has determined that the A.C.E. is operationally
and technically feasible and expects, barring unforeseen operational
difficulties that would have a significant effect on the quality of the
data, that these corrected data will be more accurate than the
uncorrected data for their intended purposes. This determination is
based on more than 20 years of Census Bureau research and experience
with coverage measurement surveys using DSE and is supported by
external experts in statistical methodology. From these years of
experience, Census Bureau statisticians have a comprehensive
understanding of the technical underpinnings of DSE. This understanding
has guided the design of the A.C.E., allowing the Census Bureau to
focus on the completeness and quality of the estimates of the
population corrected for estimated net census error.
It is possible, though very unlikely, that problems with census
operations could lead the Census Bureau to conclude that the data are
not of sufficient quality for their intended purposes. These problems
could occur in the operations leading to production of the
apportionment counts and/or in the operations leading to the production
of the corrected counts. This document does not address factors that
the Census Bureau will consider in its determination that the
apportionment counts are of sufficient quality to be used for their
intended purposes. Because this document does focus on the feasibility
of using statistical methods to improve the accuracy of Census 2000 for
purposes subsequent to the production of apportionment counts, it
discusses the review process for the final decision on whether to
release statistically corrected data. This review process will be based
on a determination of whether the A.C.E. operations were conducted in a
way that met expectations. In the fall of 2000, the Census Bureau will
present this review process to the statistical community and other
interested parties.
Background and Overview
Census data are critically important in achieving equitable
political representation and fair allocation of resources. Finding and
enumerating approximately 275 million individuals in the correct
location is, of course, an extremely challenging task. The traditional
decennial census misses certain identifiable population groups at
greater rates than others and therefore contains inherent inaccuracies.
The Census Bureau designed the Accuracy and Coverage Evaluation
(A.C.E.) using proven statistical methodologies to correct for this
differential undercount and thereby make the census more accurate.
Uses of Decennial Census Data
The Constitution requires that a census of the nation's population
be taken every 10 years to reapportion seats in the House of
Representatives,\1\ but the information provides more than just state-
by-state population totals. State and local governments use census data
to draw legislative districts of equal population to comply with the
constitutional ``one-person-one-vote'' mandate and the statutory
requirements of the Voting Rights Act. The federal government
distributes billions of dollars in grants according to population-based
formulae that rely on census data. Federal, state, local and tribal
officials study the patterns of detailed census data before
constructing hospitals, highways, bridges, and schools. Businesses,
large and small, have come to depend on the Census Bureau's population,
income, education, and housing data to make informed decisions about
locating new offices, shops, and factories, and finding markets for new
products and services. Census data also serve as definitive benchmarks
for many of the household surveys conducted by federal agencies.
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\1\ Constitution, Art. I, Sec. 2, cl. 3.
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As will be explained in more detail below, the Census Bureau has
designed the A.C.E. so that it will produce statistically corrected
census data down to the block level. Census blocks are the ``building
blocks'' employed by users of census data. The Census Bureau does not
define the aggregations employed by data users; it provides the data
that users can tabulate as needed for their programmatic purposes. For
example, an administrator distributing funds under the Elementary and
Secondary Education Act might need to distribute funds tabulated to
school districts, which can range in size from large counties and
cities to small towns and districts, while a state official responsible
for redistricting might need to aggregate and re-aggregate census
blocks into many different configurations to satisfy the requirements
of the Voting Rights Act, 42 U.S.C. Sec. 1971 et seq.
[[Page 38376]]
The A.C.E. was designed to accommodate the needs of data users by
allowing them to aggregate census blocks as appropriate for their
particular program purposes. The accuracy of aggregated census data is
more important than the accuracy of any particular block because data
users rely on aggregated data, not block-level data.\2\ Different types
of accuracy and how they can be assessed at various levels of
aggregation are reviewed below.
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\2\ The National Academy of Sciences agrees that accuracy at the
block level is not an appropriate criterion of accuracy, that
accuracy should be evaluated at aggregated levels. See Andrew A.
White and Keith F. Rust, eds., Preparing for the 2000 Census:
Interim Report II (Washington, D.C.: National Academy Press, 1997),
11-12.
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This recitation of the uses of census data illustrates the
importance of taking as accurate a census as possible by reducing the
differential undercounts of geographic areas and demographic groups.
The belief that the census should be as accurate as possible has
motivated the Census Bureau for more than 20 years to develop
techniques to reduce the differential undercount.
The Differential Undercount
The Census Bureau has documented and measured a substantial
differential undercount since the 1940 census.\3\ After the 1940
census, Census Bureau statisticians and academic researchers refined a
statistical technique known as Demographic Analysis, a technique that
measures coverage trends as well as differences in coverage by age,
sex, and race. Demographic Analysis uses records and estimates of
births, deaths, immigration, emigration, and Medicare enrollments to
develop estimates of the population at the national level,
independently from the census. Demographic Analysis, though not without
its errors, reveals the persistence of the differential undercount that
exists between the Black and the non-Black populations. The following
table illustrates this differential:
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\3\ Bureau of the Census, ``Report to Congress--The Plan for
Census 2000,'' originally issued July 1997, revised and reissued
August 1997, 2-6.
Demographic Analysis Estimates of Percentage Net Undercount, by Race: 1940-1990
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1940 1950 1960 1970 1980 1990
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Percent:
Total..................................... 5.4 4.1 3.1 2.7 1.2 1.8
Black..................................... 8.4 7.5 6.6 6.5 4.5 5.7
Non-Black................................. 5 3.8 2.7 2.2 0.8 1.3
Percentage Point Difference:
Black/Non-Black........................... 3.4 3.6 3.9 4.3 3.7 4.4
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Source: J.G. Robinson and others, ``Estimates of Population
Coverage in the 1990 United States Census Based on Demographic
Analysis,'' Journal of the American Statistical Association 88,
(September 1993): 1065.
The 1990 census revealed that the Black population was not the only
group undercounted differentially. Children were much more likely than
adults to have been undercounted in the 1990 census. While children
under the age of 18 represented 26 percent of the total national
population that year, they accounted for 52 percent of the net
estimated undercount as estimated by the 1990 Post-Enumeration Survey
(PES).\4\ Another characteristic that affected the likelihood of being
missed in the census was tenure, whether one rents or owns. Renters
were more likely to have been left out of the 1990 count. The 1990 PES
found higher undercounts among renters than for owners.\5\ As the chart
below demonstrates, a substantial differential undercount also was
estimated in 1990 for Hispanics and American Indians on reservations:
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\4\ Ibid., 3.
\5\ Howard Hogan, ``The 1990 Post-Enumeration Survey: Operations
and Results,'' Journal of the American Statistical Association 88
(September 1993): 1054, Table 3.
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[[Page 38377]]
[GRAPHIC] [TIFF OMITTED] TN20JN00.006
Within each demographic group, the undercount for renters was
considerably higher than for owners. For example, the estimated
undercount was 6.5 percent for Black renters versus only 2.3 percent
for Black owners.\7\
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\6\ Bureau of the Census, ``Assessment of Accuracy of Adjusted
Versus Unadjusted 1990 Census Base for Use in Intercensal
Estimates,'' Report of the Committee on Adjustment of Postcensal
Estimates,'' 7 August 1992, Attachment 3A, Table 2, later referred
to as CAPE; and Bureau of the Census, ``Report to Congress--the Plan
for Census 2000,'' 4.
\7\ Hogan, ``The 1990 Post-Enumeration Survey: Operations and
Results,'' 1054, Table 3.
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The differential undercount is a longstanding problem and one that
the Census Bureau has not been able to solve despite increased efforts
and resources. The National Academy of Sciences has calculated that the
per housing unit cost of the census, in 1990 constant dollars,
increased from less than $10 per housing unit in 1960, to $11 per
housing unit in 1970, to $20 per housing unit in 1980, and to $25 per
housing unit in 1990.\8\ This steady increase in unit cost from 1960 to
1990, in large part due to increased efforts to reduce coverage errors,
did not result in any appreciable reduction in the differential
undercount.
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\8\ Barry Edmonston and Charles Schultze, eds., Modernizing the
U.S. Census (Washington, D.C.: National Academy Press, 1995), 44.
The cost for Census 2000 is currently estimated to be over $50 per
housing unit in current dollars, indicating the increasingly greater
cost of taking a census using traditional methods.
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The differential undercount clearly affects census accuracy. When
identified areas and demographic groups are differentially
undercounted, the relative population shares across states and sub-
state areas are incorrect. Census data also provide the foundation for
a large number of federal demographic statistics and household
statistical surveys. These data are also extensively used by the
private sector. Inaccuracies in the decennial census are carried over
into these many other statistical series, and therefore, the persistent
differential undercount has far-reaching consequences across public and
private sector programs based on census data.
Summary of Census 2000 Operations
The Supreme Court determined in 1999 that Title 13 statutorily
precludes the use of sampling to produce congressional apportionment
counts.\9\ Accordingly, the plan for Census 2000, as outlined in the
Updated Summary: Census 2000 Operational Plan (February 1999), is to
produce apportionment numbers without the use of statistical sampling
by January 1, 2001. Rather than conducting the Integrated Coverage
Measurement (ICM) survey \10\ to produce statistically corrected
numbers as part of the original Census 2000 plan, the plan now includes
the A.C.E., which will produce statistically corrected numbers for non-
apportionment uses of the data.
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\9\ Department of Commerce v. House of Representatives, 119
S.Ct. 765 (1999).
\10\ The Census Bureau's original plan to use sampling was to
conduct an Integrated Coverage Measurement (ICM) survey to produce a
one-number census through the use of statistical sampling (``Report
to Congress--The Plan for Census 2000,'' 29-32). The Census Bureau
dropped its plans to conduct an ICM after the Supreme Court ruled
that sampling could not be used to produce the apportionment counts.
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Within the constraint of the 1999 Supreme Court decision, the
Census Bureau is committed to producing the most accurate data possible
without the use of sampling for purposes of apportionment. The
constraint does not apply to non-apportionment uses, and the Census
Bureau also remains committed to producing the most accurate data
possible for these other uses by implementing the A.C.E. As a prelude
to the discussion of the A.C.E., this paper will briefly review basic
census operations to be conducted prior to the A.C.E. A more extensive
explanation of the operations for Census 2000 can be found in the
Census 2000 Operational Plan.
The Census Bureau uses three basic data collection methods:
mailout/mailback (where the Census Bureau mails questionnaires to
housing units on the address list and the residents mail them back),
update/leave (where Census Bureau workers deliver questionnaires at the
same time they update the address list, and the residents mail them
[[Page 38378]]
back), and list/enumerate (where Census Bureau enumerators create the
address list while canvassing their assignment areas and conducting
interviews with respondents). Individuals can also respond to the
census through the Internet or by telephone. The Be Counted program
provides an additional means for people to be included in the census by
allowing them to fill out a blank form made available in various public
locations. Special enumeration procedures are followed for remote parts
of Alaska, for locations containing a concentration of persons with a
transient lifestyle (e.g., trailer parks, marinas, and campgrounds),
for group quarters (e.g., prisons and long-term care facilities), and
for people with no usual residence.
After allowing a reasonable amount of time for respondents to mail
back their questionnaires, the Census Bureau conducts an operation
called nonresponse followup (NRFU), which involves conducting a field
followup of housing units that do not return their questionnaires by
mail. A census enumerator will make up to six attempts to contact
housing units that appear occupied to secure an interview. If an
interview cannot be obtained, the enumerator attempts to interview a
proxy respondent, that is, a neighbor, rental agent, building manager,
or other knowledgeable individual.
A number of other operations are being implemented to ensure as
complete coverage as possible in the initial enumeration. Computer
edits are performed on mail-return questionnaires to identify those
that may contain missing persons and those that contain large
households (more than six persons). Interviewers conduct telephone
interviews with these households during the coverage edit followup
operation in order to obtain accurate data about the persons residing
there. Another operation, coverage improvement followup, is conducted
after NRFU. This operation includes an interviewer recheck of housing
units classified as vacant or nonexistent during NRFU to ensure that no
units have been misclassified. Finally, all major operations of the
Census 2000 plan are subjected to enhanced quality assurance (QA)
activities designed to detect and correct errors before they affect
accuracy or data quality.
The Census Bureau also designed and implemented an enhanced
marketing and partnership program that provides an integrated
communications effort to increase both awareness of the decennial
census and public cooperation. The marketing program is designed around
the first-ever paid advertising campaign, including a national media
campaign aimed at increasing mail response, targeted advertising
directed at raising mail response among historically undercounted
populations, and special advertising messages and campaigns targeted to
hard-to-enumerate populations. In the partnership program, the Census
Bureau is working nationwide with state and local partners to encourage
all individuals to respond to the census.
After the data collection efforts have been completed, the data are
processed through a number of computer operations for unduplication of
multiple responses for the same housing unit and for editing of
inconsistent or missing responses. For items that are not reported by
respondents, the Census Bureau uses the statistical process of
imputation to determine a response. The data are then tabulated, and
the tabulations and other statistical aggregations are released.
The Accuracy and Coverage Evaluation Methodology
Following the initial census, the Census Bureau will conduct the
A.C.E. Key components of the A.C.E. include the sample design, the
survey itself, and the Dual System Estimation (DSE) used to compute the
estimates of the true population.\11\
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\11\ A more extensive description of the A.C.E. can be found in
Howard Hogan's paper, ``Accuracy and Coverage Evaluation: Theory and
Application'', prepared for the February 2-3, 2000, DSE Workshop of
the National Academy of Sciences Panel to Review the 2000 Census;
and Bureau of the Census, ``Accuracy and Coverage Evaluation:
Overview of Design'', by Danny R. Childers and Deborah A.
Fenstermaker, DSSD Census Procedures and Operations Memorandum
Series S-DT-02, 11 January 2000.
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The A.C.E. in Brief
The A.C.E. methodology planned for Census 2000 involves comparing
(matching) the information from an independent sample survey to initial
census records. In this process, the Census Bureau conducts field
interviewing and computerized and clerical matching of the records.
Using the results of this matching, the Census Bureau will apply the
statistical methodology of DSE (described below) to develop coverage
correction factors for various population groups. The results will then
be applied to the census files to produce all required Census 2000
tabulations, other than apportionment. The A.C.E. can be summarized as
follows:
<bullet> Select a stratified random sample of blocks for the A.C.E.
<bullet> Create an independent list of housing units in the sample
of A.C.E. blocks.
<bullet> Begin conducting telephone interviews of mail return
housing units on a subset of the independent list.
<bullet> After the initial census nonresponse followup, conduct a
personal visit interview at every housing unit on the independent list
not already interviewed by telephone.
<bullet> Match the results of the A.C.E. interview to the initial
census.
<bullet> Resolve cases that may not match but that require
additional information by conducting a personal visit followup
interview.
<bullet> Use information from other similar people to impute
missing information.
<bullet> Categorize the A.C.E. data by age, sex, tenure, and other
appropriate predefined variables into groupings called post-strata.
<bullet> Calculate the coverage correction factors using DSE, that
is, determine the extent to which people in each post-stratum have been
over- or undercounted by the initial census.
<bullet> Apply the coverage correction factors to correct the
initial census data.
<bullet> Tabulate the statistically corrected census results.
The Sample Design
For the 2000 A.C.E., the Census Bureau selected a stratified random
sample of blocks designed to be representative of racial and ethnic
composition; tenure (owner or renter); and other variables. The sample
consists of approximately 11,800 block clusters with approximately
314,000 housing units. The sample is designed to provide sufficient
precision to estimate the true population for groupings of the
population known as post-strata. Each person belongs to one and only
one post-stratum. Post-strata are constructed with the goal of grouping
individuals who have a similar probability of having been included in
the initial census. Census 2000 post-stratification variables include
race, ethnicity, age, sex, tenure, mail return rate, and metropolitan
status/census enumeration method. For example, one post-stratum would
include non-Hispanic Black males, aged 18-29, in non-owner units, in
mailout/mailback areas of metropolitan statistical areas with 500,000
or more population, in tracts with a low mail return rate in the
census. By comparing the estimated true population based on the dual
system estimate for each post-stratum to the number of individuals
counted in the initial census enumeration for each post-stratum, the
Census Bureau estimates over- and undercounts for each post-stratum.
[[Page 38379]]
Conducting the Survey
Essential to the proper conduct of the A.C.E. is the need to ensure
that the A.C.E. and the initial census are operationally independent.
Independence requires that the probability of a particular household or
person being included in the A.C.E. is not affected by the initial
census operations and that the probability of people being included in
the initial census is not affected by A.C.E. operations. Such
independence is a critical criterion for DSE.
The A.C.E. independent interview is conducted by separately hired
and trained staff through the use of Computer Assisted Personal
Interviewing (CAPI) either by telephone or in person. CAPI is a method
of data collection using a laptop computer in which the questions to be
asked are displayed on the screen and responses are entered directly
into the computer. The Census Bureau expects that the use of CAPI will
improve the accuracy of the A.C.E. interview. To get an early start for
the A.C.E. interviewing, where possible, a telephone interview using
CAPI may be conducted for households where the census questionnaire has
been completed and for which a telephone number was obtained. This
activity is carried out concurrently with the initial census followup
of nonresponse households. The door-to-door interviewing with CAPI does
not begin until the initial census nonresponse followup is nearly
completed in a given block cluster. The A.C.E. enumerators will attempt
to secure an in-person interview with a household member. If the
interview cannot be obtained, the enumerator will interview a proxy
respondent.
After the A.C.E. independent interviews have been completed,
computer matching between the initial census and the A.C.E. person
records is carried out, followed by a clerical matching operation using
an automated review system. The matching process allows the Census
Bureau to determine who may have been missed by the initial census or
to determine erroneous enumerations. It should be noted that the census
can miss either entire households or individuals within households.
This is also the case for erroneous enumerations.
The Census Bureau has carefully designed the A.C.E. to minimize
matching errors. Incorrect matching generally results either from
errors caused by incomplete, inaccurate, or conflicting data, or from
errors where a poor match decision was made even though the data were
sufficient. It is critical that the matching be as accurate as
possible. Accordingly, as necessary, the Census Bureau conducts a
personal visit follow-up operation to obtain the additional information
needed to accurately code A.C.E. and census nonmatches. After this
followup, the Census Bureau conducts a final clerical matching
operation.
Even after this intense effort, occasionally some information will
still be missing, either person characteristics, status of enumeration
in the initial census, or match status for A.C.E. cases that could not
be resolved. Before any calculations can be made to determine the
estimated true population, missing person characteristics, initial
census enumeration status, and A.C.E. match status must be resolved.
Missing person characteristics such as age, race, sex, and tenure are
statistically imputed from data reported for other household members or
from similar households in the geographic area. For unresolved cases,
the Census Bureau uses statistical imputation methodology to impute
probabilities of being correctly enumerated or matched. The Census
Bureau then estimates the true population by using these results in
Dual System Estimation.
Dual System Estimation
DSE is an established and accepted statistical technique that is
also referred to as ``capture/recapture.'' \12\ Because the Census
Bureau has conducted years of research into the likelihood that people
of varying characteristics will be included in the census enumeration
(this likelihood is known as inclusion probability), it is able to
divide the nation's population into post-strata. Each post-stratum is
defined so as to contain people with a similar probability of being
included in the initial census. At the conclusion of the A.C.E.
processes described previously, data are available for each post-
stratum to calculate a dual system estimate.\13\
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\12\ Michael L. Cohen, Andrew A. White, and Keith F. Rust,
Measuring a Changing Nation--Modern Methods for the 2000 Census
(Washington, D.C.: National Academy Press, 1999), 31; and Kirk M.
Wolter, ``Some Coverage Error Models for Census Data,'' Journal of
the American Statistical Association 81 (June 1986): 338.
\13\ Production of these estimates is discussed in more detail
in Bureau of the Census, ``Accuracy and Coverage Evaluation Survey:
Dual System Estimation,'' by Donna Kostanich and Richard Griffin,
DSSD Census 2000 Procedures and Operations Memorandum Series #Q-20,
12 January 2000.
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The dual system estimate is an estimate of the true population
total for each post-stratum. The dual system estimates are then used to
calculate a coverage correction factor for each post-stratum. The
coverage correction factor is a ratio of the dual system estimate (the
estimate of the true population) to the initial census count. These
factors are then applied to correct the initial census data files. For
example, if the coverage correction factor for non-Hispanic Black
males, aged 18-29, in non-owner units, in mailout/mailback areas of
metropolitan statistical areas with 500,000 or more population, in a
tract with a low mail return rate in the census, is 1.02, then for
every 100 such person records counted in the census in those areas, two
numerical records will be added. Once these factors are applied, the
corrected population estimates are created and tabulated.
Assessment of Feasibility
Section 195 of the Census Act states that ``the Secretary shall, if
he considers it feasible, authorize the use of sampling,'' but the term
``feasible'' is not defined. As discussed in a legal opinion from the
Department of Commerce's General Counsel, the Census Bureau understands
this term in accordance with its ordinary meaning and the overall
purposes of Title 13. It is important to note that even if Title 13
were silent as to the obligation to use sampling if feasible, the
Census Bureau would apply criteria similar to those described below to
determine whether to correct the census through the use of statistical
sampling. The Census Bureau is committed to using reliable statistical
methods if those methods can be expected to improve the overall
accuracy of the census.
The Definition of Feasibility
The Census Bureau's determination that sampling is ``feasible'' is
based on whether its use is possible, that is, compatible with other
aspects of the census plan and with any statutory, timing, and funding
constraints. Equally important, this determination is based on whether
the use of sampling is expected to improve the overall accuracy of
census data by improving overall coverage and reducing the differential
undercount. These two components of the feasibility determination
represent operational feasibility and technical feasibility. Can the
Census Bureau produce the statistically corrected block-level numbers
by the April 1, 2001, statutory deadline? Can the statistically
corrected counts be expected to improve the overall accuracy of census
data?
More specifically, in the context of Census 2000, the use of
statistical sampling is feasible to correct the census if the two
components of feasibility, operational and technical,
[[Page 38380]]
are satisfied. Operational feasibility refers to the Census Bureau's
ability to conduct the A.C.E. with available resources and within
required deadlines or time frames. Technical feasibility refers to the
Census Bureau's expectation that the A.C.E. statistical methodology, if
carried out as planned, will improve the accuracy of the census for
non-apportionment uses of the data. As discussed below, the Census
Bureau's extensive experience with coverage measurement surveys,
including its incorporation of improvements since 1990, confirms the
conclusion that the A.C.E. is both operationally and technically
feasible.
Operational Feasibility
Operational feasibility refers to the Census Bureau's ability to
conduct each major component of the census within applicable deadlines
and with available resources. The Census Bureau expects to conduct each
major component of the census, including the A.C.E., in time to meet
the April 1, 2001, deadline for producing the redistricting data.
Release of Data Products for Use in Redistricting
The Census Bureau's goal is to produce the most accurate numbers
possible within the constraints imposed by the federal statute and
available resources. Section 141(c) of Title 13 requires the Census
Bureau to deliver redistricting numbers to the states by April 1,
2001.\14\ In past decennial censuses, the Census Bureau has been able
to release redistricting numbers to certain states prior to the federal
deadline, enabling redistricting officials in those states to meet
deadlines set by state statutes and constitutions. The Census Bureau
will, as in the past, release the numbers from Census 2000 to the
states as they are ready, giving priority to states that need to meet
early deadlines.
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\14\ The Census Bureau's FY 1998 Appropriations Bill (P.L. 105-
119) requires the Census Bureau, when it releases redistricting
numbers based on statistical methods, to also release data produced
without the use of statistical methods at all levels of geography.
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Operational Considerations
The Census Bureau's detailed plan for carrying out the entirety of
the census operation, including the A.C.E., is set forth in the
``Master Activity Schedule'' (MAS).\15\ This plan has undergone
thorough reviews and analyses and supports the Census Bureau's
confidence that it can implement the A.C.E. methodology correctly and
successfully. The Census Bureau introduced its original Census 2000
plan in 1995. Since that time, the plan has been refined to incorporate
testing, analysis, expert and other public input, and policy and
programmatic changes, including the Supreme Court's January 25, 1999,
ruling. During the last five years, the Census Bureau has put into
place a comprehensive project management framework based on a powerful
project management tool used by some of the world's largest private
organizations. The use of this and other project tools, such as an
integrated cost model and function and process modeling software, led
to the Census Bureau's determination that it could produce the
statistically corrected numbers by April 1, 2001. A revised Census 2000
MAS, reflecting this determination, along with the Census 2000
Operational Plan, were presented to the U.S. House of Representatives
Subcommittee on the Census, as well as the Census Bureau's other
oversight and appropriations committees and subcommittees, in March
1999.
---------------------------------------------------------------------------
\15\ Bureau of the Census, ``Master Activity Schedule for Census
2000.''
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Resource Considerations
Resources are also relevant to a feasibility determination. Based
on current FY 2000 appropriations and the anticipation that the
Administration's FY 2001 budget request for Census 2000 will be
appropriated, the Census Bureau should be able to hire sufficient staff
and acquire the necessary equipment to complete Census 2000 and produce
statistically corrected redistricting numbers by the April 1, 2001,
statutory deadline.
The Census 2000 Dress Rehearsal
In preparing for Census 2000, the Census Bureau, as has been its
practice for many decades, conducted a dress rehearsal, or full-scale
census simulation, in several sites across the country.\16\ The dress
rehearsal demonstrated the operational feasibility of producing the
statistically corrected block-level data by the statutory deadline. The
Census Bureau was able to produce data without the use of statistical
sampling within nine months (as it is required to do for apportionment)
and statistically corrected data within 12 months (as it is required to
do for redistricting).
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\16\ Sacramento, California; Menominee County, Wisconsin; and
Columbia, South Carolina and 11 surrounding counties.
---------------------------------------------------------------------------
Technical Feasibility
Technical feasibility refers to whether the statistical methodology
used by the A.C.E. will improve accuracy. Measuring the accuracy of the
census is not a simple task. There are two types of accuracy--numeric
and distributive--central to census operations and the uses of census
data. Starting with the planning for the 1980 census, the Census Bureau
has developed, tested, refined, and implemented statistical methods to
improve both the numeric and distributive accuracy of the census
enumeration, culminating in the 2000 A.C.E. design. The Census Bureau
expects the A.C.E. to improve both numeric and distributive accuracy.
Defining Numeric and Distributive Accuracy
In analyzing the effect of the A.C.E. on accuracy, this discussion
focuses on the accuracy of population totals for geographic areas and
demographic groups, and, though important in the overall understanding
of the census, not on the accuracy of detailed characteristic data for
people or housing units.
Numeric accuracy refers to how close the overall count of a
particular geographic area or demographic group is to the ``truth,''
that is, to the actual number of people who reside in that area or
belong to that group. Distributive accuracy refers to how close the
relative proportion or share of a geographic area or demographic group
is to its true share relative to other areas or groups. A census
operation that increases numeric accuracy moves the overall count for
any particular area or demographic group closer to the true total. For
example, an operation that enumerates individuals in a particular state
who would otherwise be missed, increases the numeric accuracy of that
state. A census operation that increases distributive accuracy will
improve the accuracy of the population share for a given area or
demographic group compared to other areas or demographic groups `` in
other words, improve the accuracy of the estimated proportions or
shares of the total population for the areas or groups.
A perfect census--one in which every resident is counted once and
only once and is correctly located--would be both numerically and
distributively accurate. But, as noted above, the Census Bureau's
experience leads it to expect that, absent statistical correction,
Census 2000 will result in both a net national undercount and various
differential undercounts. Such undercounts affect both numeric and
distributive accuracy. Although much of the analysis of the 1990 census
focused on distributive accuracy, both types of accuracy are important
and must be considered in designing a census that
[[Page 38381]]
will provide the most accurate count possible.
Importance of and Relationship Between the Two Types of Accuracy
The decennial census can be viewed as one of the nation's most
important civic ceremonies. Viewed in this broad perspective, securing
maximum participation must be a key Census Bureau goal. To the extent
that the census has the obligation to fully reflect who Americans are
and how they live, everyone should be counted. Census operations that
improve numeric accuracy, irrespective of their impact on distributive
accuracy, meet this most basic goal.
In contrast, census operations that improved distributive accuracy
but left many residents out of the count would not meet this basic
goal. For example, a census that counted 90 percent of every
demographic group in every geographic area would be distributively
accurate, but would fail the obligation of the census to include
everyone.
Numeric accuracy of census data is particularly important when
population thresholds determine eligibility for program funding. For
example, in FY 1998, the U.S. Department of Housing and Urban
Development obligated over $3 billion under its Community Development
Block Grants Entitlement Program. For this program, the population
thresholds used are central cities of metropolitan statistical areas;
other cities over 50,000 in metropolitan statistical areas; and
qualified urban counties of at least 200,000 (excluding the population
in entitlement cities located within the boundaries of such counties).
Central city and metropolitan statistical area designations themselves
depend upon certain population thresholds.
Additional uses of census data for which numeric accuracy is
critical are associated with the Census Bureau's intercensal population
estimates and survey controls. Decennial census data are the base for
the Census Bureau's intercensal population estimates and projections
programs, programs that produce annual population estimates for all
general purpose governments and projections for the nation and states,
respectively. Specific uses of the population estimates that depend on
numeric accuracy include use of the estimates as controls for many
federal surveys, including the Current Population Survey (which
provides monthly labor force and employment data), and as denominators
for many critical federal data series, such as birth, mortality, and
cancer rates, as well as per capita income.
For the purpose of reapportioning seats in the House of
Representatives, distributive accuracy becomes a principal concern,
because reapportionment is based on a proportionate allocation formula.
Federal and state redistricting are based on criteria for dividing
state populations into districts of equal size; thus both numeric and
distributive accuracy are important. Distributive accuracy is also
central to federal funding allocations that distribute funds based on
relative percentage of the population.
The goal of the Census Bureau is to conduct a census that is both
numerically and distributively accurate. This said, it is numeric
accuracy that drives the process for designing Census 2000 operations
other than the A.C.E. When it designs a decennial census, the Census
Bureau has available a very large number of possible operations. It
assesses these operations against such criteria as cost, statutory
deadlines, whether the staff necessary to implement these operations
can be recruited and adequately trained, and how well the operations
fit with other operations under consideration. In this extensive
process of evaluating individual operations and then assembling them in
the final design, there is one paramount criterion: what census design
has the highest probability of correctly enumerating the population?
That is, can an operation considered separately, and when combined with
other operations, be expected to help the Census Bureau correctly count
as many people as possible, given funding, timing, and other
constraints?
Obviously, if perfect numeric accuracy were achieved for all
geographic areas and demographic groups, then perfect distributive
accuracy would also result. However, because it is difficult and
perhaps impossible to know a priori the effects of a particular census
operation on distributive accuracy, assessing an operation's effect on
distributive accuracy can rarely be part of the planning process. The
difficulty of designing operations for distributive accuracy is
compounded if it is to be achieved across geographic areas and multiple
demographic groups and then simultaneously across many levels of
geography. For example, the Local Update of Census Addresses program,
being voluntary, may have benefitted communities with strong local
planning departments more than other communities. This program, then,
had an unpredictable effect on distributive accuracy.
In principle, any given census operation designed to increase
numeric accuracy can increase distributive accuracy, leave it the same,
or make it worse. But in assembling a census design, the Census Bureau
does not reject operations that would improve numeric accuracy (and
meet other criteria for inclusion) even though such operations might
affect distributive accuracy negatively, or indeterminately. For
example, the Census Bureau has developed for Census 2000 an extensive
partnership program to assist local jurisdictions and community
organizations in promoting participation in the census. But increasing
the counts for these participating localities will not necessarily
translate into improvements in distributive accuracy. If one state
promotes the census more effectively than another state, the state with
the better promotion program may earn a higher share of the total
national population than would otherwise be the case.
Although the Census Bureau has largely targeted its coverage
improvement programs in the areas that have been the most difficult to
count, it has not rejected census operations that might
disproportionately improve the count for groups that are already well
counted. An example of the latter in Census 2000 is the ``New
Construction'' program.\17\ Moreover, the Census Bureau has supported
the efforts of neighborhoods, cities, and states to increase the
accuracy of their census counts, irrespective of the effect on
distributive accuracy. The Census Bureau views these increases in
numeric accuracy, even for well counted groups, as important to the
most basic goal of the census--counting everyone.
---------------------------------------------------------------------------
\17\ In this program, local and tribal governments liaisons in
mailout/mailback areas review the Census Bureau's address list for
their areas and provide the agency with the addresses of all newly
constructed housing units as of April 1, 2000. The Census Bureau
matches these addresses to its address list, updated with United
States Postal Service files, and verifies and enumerates those
addresses that are not on its address list.
---------------------------------------------------------------------------
Finally, although different uses of census data depend to varying
degrees on each type of accuracy, the two concepts are related. When
the census falls short of overall numeric accuracy, states and
localities with large populations that are differentially undercounted
will suffer a diminution in proportionate shares. For example, the
differential undercount in the 1990 census caused states and localities
with large minority populations to suffer a diminution in share. The
Census Bureau can and does try to improve both
[[Page 38382]]
numeric and distributive accuracy by bringing the total count for each
area or demographic group closer to its true count.
Impact of the A.C.E. on Accuracy
The preceding discussion of accuracy included a discussion of the
design of the census for apportionment purposes, but did not consider
the effects of the A.C.E. on numeric and distributive accuracy. As
discussed below, the A.C.E. measures and corrects for the deficiencies
in the initial census, and consequently the Census Bureau expects that
the A.C.E. will improve both distributive and numeric accuracy.
Based on decades of research identifying and measuring the
undercount, as well as the 1990 census evaluations (discussed below),
the Census Bureau expects the differential undercount to persist in
Census 2000, with properties similar to those measured in 1990.\18\
This extensive research into measuring and correcting the differential
undercount, augmented by enhancements to prior coverage measurement
surveys, leads the Census Bureau to expect that the A.C.E. will improve
accuracy. The A.C.E. is expected to improve numeric accuracy by moving
total counts closer to the true count and to improve distributive
accuracy by more accurately counting areas that contain significant
populations of historically undercounted groups.
---------------------------------------------------------------------------
\18\ This conclusion is based on the assumption that the
coverage improvement programs used for Census 2000 will have similar
results as those used in 1990.
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It is important to consider the contribution of the A.C.E. to
numeric and distributive accuracy at different levels of geography. The
Census Bureau expects that the A.C.E. will, on average, improve numeric
accuracy for geographic areas down to and including census tracts.\19\
``On average'' means that, while some tracts will be more numerically
accurate using uncorrected numbers and others more accurate using
corrected numbers, the average effect over all tracts is greater
accuracy with than without the A.C.E. The Census Bureau also expects
that improvement will be greatest for those areas that contain groups
that have been historically undercounted.
---------------------------------------------------------------------------
\19\ Bureau of the Census, ``Report to Congress--The Plan for
Census 2000,'' 44-46. Census tracts are small, homogeneous,
relatively permanent statistical subdivisions of counties formed for
the purpose of collecting and tabulating decennial census data.
Tracts typically contain between 1,000 and 8,000 people.
---------------------------------------------------------------------------
Regarding distributive accuracy, the Census Bureau's extensive
evaluations following the 1990 census led it to conclude that the 1990
PES would have, on average, increased distributive accuracy for larger
geographic areas, including states and cities and counties with more
than 100,000 people. These evaluations did not determine whether the
1990 PES would have improved the distributive accuracy of smaller
geographic areas.\20\ In addition, these evaluations did not address
whether the unadjusted counts were more accurate for these areas. The
research on these issues conducted by the Census Bureau's Committee on
Adjustment of Postcensal Estimates (CAPE) is discussed more fully
below. Based on this research, the Census Bureau expects the
incorporation of the A.C.E. results in the Census 2000 counts to have a
similar effect, that is, to improve distributive accuracy for larger
geographic areas, as in 1990.
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\20\ When apportionment is calculated based on Census 2000
counts, the average Congressional District is expected to be over
600,000 people.
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Historical Experience With Coverage Measurement Surveys
Demonstrates Feasibility
The Census Bureau has a longstanding practice of employing
scientific sampling techniques in the decennial census whenever
sampling has the potential to lower costs without negatively affecting
quality.\21\ It has devoted substantial resources for over two decades
to the development of coverage measurement programs employing high
quality sampling methodologies that enable the production of more
accurate data. The feasibility assessment discussed in this document is
one more logical step along that continuum.
---------------------------------------------------------------------------
\21\ The Census Bureau first used sampling in a decennial census
in 1940, in the program now known as ``long form'' enumeration,
which is used to obtain detailed demographic information. The Census
Bureau has used sampling to conduct federal surveys to collect key
information, including unemployment and labor force data, etc., for
many decades.
---------------------------------------------------------------------------
The Census Bureau and leading professional statistical
organizations have concluded that the best way to address the
persistent problems of the undercount and the differential undercount
is to complement traditional enumeration procedures with scientific
sampling, using DSE. Extensive research, testing, and refinement of the
tools of statistical adjustment have led the Census Bureau to determine
that the A.C.E. will improve the overall accuracy of the census.
The Census Bureau also has used Demographic Analysis to evaluate
coverage in decennial censuses and broadly validate the coverage
measurement survey results.\22\ Since independent Demographic Analysis
estimates are not available below the national level, nor have
estimates been available for detailed demographic groups (for example,
tenure or detailed racial groups), the Demographic Analysis method has
not been used to adjust the census for undercoverage.
---------------------------------------------------------------------------
\22\ J.G. Robinson and others, ``Estimates of Population
Coverage in the 1990 United States Census Based on Demographic
Analysis,'' Journal of the American Statistical Association 88
(September 1993): 1061-77.
---------------------------------------------------------------------------
The 1980 Census Experience
Development of the modern coverage measurement survey began with
the 1980 Post Enumeration Program, or PEP.\23\ The PEP was a coverage
measurement survey, based on DSE methodologies, designed to evaluate
the accuracy of the 1980 census. Over 50 lawsuits were filed regarding
the 1980 census, most contending that the results of the PEP should
have been used to adjust the census. However, the PEP had been designed
primarily as a coverage evaluation tool, rather than an adjustment
mechanism, making its use to correct the census results problematic.
The Director of the Census decided not to adopt the numbers produced
from this first attempt at statistical correction using DSE, judging
the estimates to be flawed by missing and inaccurate data.\24\
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\23\ For a detailed discussion of the 1980 Census Post
Enumeration Program, see Robert E. Fay and others, The Coverage of
Population in the 1980 Census (Washington, D.C.: Government Printing
Office, 1988), 37-92.
\24\ Department of Commerce, ``Position on Adjustment of the
1980 Census Counts for Underenumeration,'' Federal Register (16
December 1980) vol. 45, no. 243, p. 82872.
robop...@us.govnews.org
Posting-number: Volume 65, Issue 119, Page 38373, Part 1
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Significantly, however, the PEP operation provided a wealth of
information on measuring coverage in a census using DSE. The PEP
illustrated the potential use of coverage measurement surveys as a
coverage evaluation tool for U.S. censuses. It was clear in principle
that coverage measurement surveys could be used to correct the census.
In the two subsequent decades, the Census Bureau built upon the
knowledge and experience gained in the 1980 census.
Early Research and Development for the 1990 Census
After the 1980 experience, the Census Bureau began an extensive
review of its coverage measurement program to enhance the methods that
had been used in 1980 and to determine the feasibility of a statistical
adjustment in 1990. Adjustment of the census was a topic of lively
debate in the statistical
[[Page 38383]]
community during the 1980s. Census Bureau professionals and outside
statisticians published more than 100 papers on coverage measurement
issues.\25\ In 1983, the Census Bureau formed the Undercount Research
Staff, a staff of agency professionals charged with addressing coverage
measurement issues and with assessing the potential correction of the
1990 census. This group conducted research over the decade leading up
to the 1990 census.
---------------------------------------------------------------------------
\25\ See Tommy Wright and Joyce Farmer, ``A Bibliography of
Selected Statistical Methods and Development Related to Census
2000,'' 3rd ed., 1 May 2000, for a list of many of the most
significant of these papers.
---------------------------------------------------------------------------
Planning for the 1990 census progressed with a two-track approach--
preparing to take the best traditional enumeration possible, while
simultaneously developing a Post-Enumeration Survey (PES), a coverage
measurement survey the results of which could be used to statistically
correct the census. The Census Bureau's position was that it would
proceed with correction if it could determine, prior to the spring of
1987, that implementation of a PES-based correction was feasible. As
part of its research effort, the Census Bureau carried out the Test of
Adjustment Related Operations (TARO) in 1986. Based on the results of
the TARO, as well as various theoretical and empirical studies
conducted since 1980, senior statisticians at the Census Bureau
concluded that statistical methods existed that could produce census
counts with a reduced differential undercount, and that if funded and
successfully completed, the program incorporating these methods could
be used to statistically correct the 1990 census.\26\
---------------------------------------------------------------------------
\26\ Dan Childers and others, ``The Technical Feasibility of
Correcting the 1990 Census,'' in Proceedings of the Social
Statistics Section of the American Statistical Association Held in
San Francisco, California, 17-20 August 1987.
---------------------------------------------------------------------------
As discussed below, the Department of Commerce overruled the Census
Bureau and decided not to allow adjustment of the 1990 census. The
Census Bureau's research on the PES as a coverage measurement tool
continued, including the conduct of the 1988 dress rehearsal Post-
Enumeration Survey. The 1988 dress rehearsal demonstrated significantly
improved operations and once again demonstrated DSE's consistent
ability to measure the undercount and the differential undercount.\27\
---------------------------------------------------------------------------
\27\ Dan Childers and Howard Hogan, ``The 1988 Post Enumeration
Survey Methods and Preliminary Results,'' in Proceedings of the
Survey Research Methods Section of the American Statistical
Association Held in New Orleans, Louisiana, 22-25 August 1988.
---------------------------------------------------------------------------
Litigation Challenging Decision to Halt 1990 Adjustment-Related
Planning Activities
The Department of Commerce, in the fall of 1987, directed the
Census Bureau not to proceed with its plans to produce adjusted census
figures, prompting the filing of a lawsuit against the Department and
the Census Bureau. As part of that lawsuit, on July 17, 1989, the
Department of Commerce entered into a stipulation, vacating the
Department's 1987 decision against adjustment and requiring the
Secretary to consider de novo, after the completion of the census,
whether adjustment was warranted. The Census Bureau would conduct a PES
and certain other adjustment-related planning operations, \28\ and the
Secretary was to announce his decision on the adjustment issue by July
15, 1991. Pursuant to the stipulation, the Department of Commerce
agreed to develop and adopt promptly ``guidelines articulating what
defendants believe are the relevant technical and nontechnical
statistical and policy grounds for the decision on whether to adjust
the 1990 Decennial Census population counts.'' An adjustment would be
made if the Secretary of Commerce, in his judgment, determined that
doing so would satisfy the guidelines. The stipulation also set up a
Special Advisory Panel composed of four experts chosen by the
plaintiffs and four experts chosen by the defendants; the Panel's role
was to advise the Secretary regarding adjustment. At this time, the
Census Bureau convened the Undercount Steering Committee, a group of
senior career agency employees, and charged the committee with
evaluating the conduct of the 1990 PES and assessing the accuracy of
the adjusted versus the unadjusted census counts.
---------------------------------------------------------------------------
\28\ Prior to the Department's 1987 decision halting the Census
Bureau's adjustment-related planning activities for the 1990 census,
the agency had planned to conduct a PES of 300,000 housing units.
Under the terms of the stipulation, the Census Bureau agreed to
conduct a PES of approximately 165,000 housing units, the results of
which could be used to adjust the census.
---------------------------------------------------------------------------
The Department of Commerce published its final guidelines on March
15, 1990. \29\ The guidelines established, among other things, the
principle that the unadjusted census counts would be presumed more
accurate unless it could be shown that the adjusted counts were more
accurate at the national, state, and local levels. This presumption and
the guidelines in general will be discussed in greater detail below.
---------------------------------------------------------------------------
\29\ Department of Commerce, ``Final Guidelines for Considering
Whether or Not Statistical Adjustments of the 1990 Decennial Census
of Population and Housing Should be Made for Coverage Deficiencies
of the Population,'' Federal Register (15 March 1990) vol. 55, p.
9838.
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Conducting the 1990 Census and Deciding Against Adjustment
The Census Bureau applied the DSE methodology in the 1990 PES to
produce a second set of population counts for every block in the
nation. \30\ Under the direction of the Undercount Steering Committee
the Census Bureau analyzed the PES results extensively, producing 33
separate and detailed technical reports analyzing various aspects of
the survey and its results. The Census Bureau's extensive analysis was
complemented by a large volume of outside expert analysis of the PES
results. \31\
---------------------------------------------------------------------------
\30\ Hogan, ``1990 Post-Enumeration Survey,'' 1054.
\31\ Wright and Farmer, ``A Bibliography of Selected Statistical
Methods Related to Census 2000.''
---------------------------------------------------------------------------
Based on the Census Bureau's analyses, then Census Bureau Director
Barbara Bryant and the majority of the Undercount Steering Committee
recommended that the 1990 census be statistically adjusted. The Special
Advisory Panel, convened as part of the stipulation, was divided in its
recommendations regarding adjustment. The panel members selected by
defendants all recommended against statistical adjustment, and the
panel members selected by the plaintiffs all recommended in favor of
adjustment. On July 15, 1991, Secretary Mosbacher announced that the
1990 decennial census would not be statistically adjusted. \32\
---------------------------------------------------------------------------
\32\ Department of Commerce, ``Adjustment of the 1990 Census for
Overcounts and Undercounts of Population and Housing: Notice of
Final Decision,'' Federal Register (22 July 1991) vol. 56, p. 33583.
---------------------------------------------------------------------------
After the Secretary announced his decision, the plaintiffs returned
to court, seeking an order compelling the Department to adjust the 1990
census. On April 13, 1993, Judge McLaughlin of the U.S. District Court
upheld Secretary Mosbacher's decision, determining that the decision
was not arbitrary or capricious, although he stated that ``were this
Court called upon to decide this issue de novo, I would probably have
ordered the adjustment.'' \33\ Judge McLaughlin noted also that ``light
of recent improvement in statistical tools and the practical benefits
that the 1990 PES has provided, the use of adjustment in the next
census is probably inevitable.'' \34\
---------------------------------------------------------------------------
\33\ City of New York v. U.S. Dept. of Commerce, 822 F. Supp.
906, 928 (E.D.N.Y. 1993).
\34\ 822 F. Supp. 906 at 918, fn. 27.
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[[Page 38384]]
Postcensal Estimates and Survey Controls Decision
Although Secretary Mosbacher determined not to adjust the 1990
census for estimated net census undercount, he deemed it appropriate
that the Census Bureau consider using the adjusted counts as the basis
for producing postcensal estimates: ``I am today requesting that the
Census Bureau incorporate, as appropriate, information gleaned from the
Post-Enumeration Survey into its intercensal estimates of the
population.'' \35\
---------------------------------------------------------------------------
\35\ Department of Commerce, ``Adjustment of the 1990 Census,''
33582.
---------------------------------------------------------------------------
Census Bureau Director Bryant convened the Committee on Adjustment
of Postcensal Estimates (CAPE) to study this issue and make
recommendations to her. CAPE was a group of senior statisticians,
demographers, and other Census Bureau professionals assembled to
conduct additional analyses of the adjusted counts. The Committee's
work extended over a 15-month period. The Committee issued a report on
August 8, 1992, and an Addendum on November 24, 1992. \36\ The Addendum
was the result of continuing and more focused analysis by the team.
Taken together, the initial CAPE report and the Addendum found that the
adjusted numbers were overall more accurate in terms of distributive
accuracy at the state level and for areas with greater than 100,000
population. For areas with populations of less than 100,000, the CAPE
could not identify any improvement in distributive accuracy for the
adjusted data. \37\
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\36\ CAPE; ``Additional Research on Accuracy of Adjusted Versus
Unadjusted Census Base for Use in Intercensal Estimates,'' Addendum
to Report of the Committee on Adjustment of Postcensal Estimates, 25
November 1992, referred to later as CAPE Addendum.
\37\ As will be discussed more fully below, more recent research
has confirmed that the Census Bureau similarly cannot determine that
the uncorrected 1990 data were more distributively accurate. For
aggregations below 100,000, the evidence as to accuracy is
indeterminate, that is, neither favoring the unadjusted nor the
adjusted counts. See Bureau of the Census, ``Analysis of CAPE
Findings on PES Accuracy at Various Geographic Levels,'' by Sally M.
Obenski and Robert E. Fay, 9 June 2000.
---------------------------------------------------------------------------
In January 1993, Dr. Bryant announced that the Census Bureau would
not use the 1990 adjusted counts as the basis for producing postcensal
estimates of the population. \38\ Director Bryant's Census decision was
made in light of, though not explicitly governed by, the litigation
guidelines that stated that adjustment was not warranted unless
improvement could be clearly demonstrated down to small levels of
geography, such as places and counties.
---------------------------------------------------------------------------
\38\ Department of Commerce, ``Decision of the Director of the
Bureau of the Census on Whether to Use Information from the 1990
Post Enumeration Survey (PES) to Adjust the Base for the Intercensal
Population Estimates Produced by the Bureau of the Census,'' Federal
Register (4 January 1993) vol. 58, no. 1, 69.
---------------------------------------------------------------------------
Recognizing the improvements in accuracy for certain uses of census
data, Dr. Bryant decided to offer sponsors of federal sample surveys
the option of having their surveys calibrated to population estimates
benchmarked to adjusted census results. \39\ Accordingly, in December
of 1993, the Bureau of Labor Statistics (BLS) requested that the Census
Bureau convert the Current Population Survey controls to ones based on
estimates incorporating the results of the 1990 PES. The BLS stated its
conviction ``that the undercount-adjusted estimates provide a more
accurate reflection of the level and distribution of the national
population and that of most States than the estimates based on the raw
Census counts.'' \40\ The BLS also requested that the population
controls for the Consumer Expenditure Survey be adjusted in a similar
fashion. \41\ Subsequent to the BLS decision, all other major national
household surveys conducted by the Census Bureau for other agencies of
the federal statistical system were converted to an adjusted population
basis. Thus, corrected data from the 1990 census are already
incorporated in many federal statistical series.
---------------------------------------------------------------------------
\39\ Ibid., 70.
\40\ Katharine G. Abraham, U. S. Bureau of Labor Statistics, to
Harry A. Scarr, U. S. Bureau of the Census, 1 December 1993.
\41\ Ibid.
---------------------------------------------------------------------------
Early Census 2000 Planning
The results of the 1990 census led the Census Bureau, other
professional statisticians, and Congress to conclude that significant
changes were required for the next census. A comprehensive re-
examination of census methodology was needed to identify a census
design that would improve the accuracy of the census. To this end, in
November 1990, the Census Bureau established the ``Task Force for
Planning for the Year 2000 Census and Census-Related Activities for
2000-2009.'' The Task Force was responsible for defining a census
design for Census 2000, considering both policy and technical issues,
and a demographic measurement system for related activities for 2000
through 2009.
In June 1992, the General Accounting Office (GAO) released a
comprehensive evaluation of the 1990 census, discussing lessons learned
and identifying opportunities for fundamental, effective reforms. The
GAO concluded that reduced data quality (including failure to make
reductions in the net and differential undercounts)'' * * * is a cost
of the current approach to taking the census * * *'' and that ``[t]he
results from 1990 demonstrate that adding more resources [while
employing traditional census-taking methods] is unlikely to allow the
Bureau to enumerate that last remaining segment of the population.''
\42\
---------------------------------------------------------------------------
\42\ General Accounting Office, Decennial Census: 1990 Results
Show Need for Fundamental Reform, Report to Congressional
Requesters, 9 June 1992, 62, 49 GAO/GGD-92-94.
---------------------------------------------------------------------------
Also at the beginning of the decade, two panels of the National
Academy of Sciences' (NAS) National Research Council were convened to
study ways to improve the census for 2000. The Decennial Census
Improvement Act of 1991, signed into law by President Bush, required
the Census Bureau to contract with the National Academy of Sciences to
study * * * the means by which the Government could achieve the most
accurate population count possible * * *'' specifically considering,
among other things, ''. . . the appropriateness of using sampling
methods in combination with basic data-collection techniques or
otherwise, in the acquisition or refinement of population data,
including a review of the accuracy of data for different levels of
geography * * *.'' \43\ The Panel on Census Requirements in the Year
2000 and Beyond was established pursuant to this statutory requirement,
supplementing the work already being performed by the NAS Panel to
Evaluate Alternative Census Methods. This latter panel was established
to provide an independent review of the technical and operational
feasibility of the design alternatives and of the tests to be conducted
by the Census Bureau. The Methods Panel's recommendations on testing
and design alternatives informed the final design of the original plan
for Census 2000. The Panel issued its final report in 1994,
recommending that the agency use sampling as an essential part of
census-taking in Census 2000. \44\
---------------------------------------------------------------------------
\43\ Congress, House, Decennial Census Improvement Act of 1991,
102nd Cong., 2nd sess., H.R. 3280, Congressional Record, daily ed.
(9 October 1991), H7694 became Public Law 102-135 on October 24,
1991. It was set forth in the commentary to Title 13, U.S. Code,
sec. 141.
\44\ Duane L. Steffey and Norman A. Bradburn, Counting People in
the Information Age (Washington, D.C.: National Academy Press,
1994), 4.
---------------------------------------------------------------------------
In June 1995, the Task Force convened at the beginning of the
decade issued final recommendations in its ``Global Report,''
suggesting a number of
[[Page 38385]]
improvements for Census 2000. \45\ The Task Force endorsed the Census
Bureau's basic plan to conduct an Integrated Coverage Measurement (ICM)
survey and suggested that the Census Bureau pursue an ICM design that
would incorporate the best features of alternative methodologies,
including DSE and CensusPlus. \46\ The Census Bureau tested these
alternate methodologies in the 1995 Census Test, concluding along with
the NAS Panel to Evaluate Alternative Census Methodologies that DSE
offered the best opportunity to produce high quality statistical
correction. \47\
---------------------------------------------------------------------------
\45\ Bureau of the Census, ``Reinventing the Census,'' Global
Report of the Task Force for Planning the Year 2000 Census, June
1995.
\46\ For a description of these methodologies and the
differences between them, see White and Rust, Preparing for the 2000
Census: Interim Report II, 48-51.
\47\ A third National Academy of Sciences panel, the Panel to
Evaluate Alternative Census Methodologies, was convened to study
ways to improve the census for 2000. In its earlier report (Andrew
A. White and Keith F. Rust, eds., Sampling in the 2000 Census:
Interim Report I (Washington, D.C.: National Academy Press, 1996)
following the 1995 Census Test, but before all the analyses from
that test had been completed, the Panel concluded that ''* * *
nothing in the [1995] census test, nor any other development,
suggests that a decennial census that * * * reduces differential
undercoverage can be conducted without the use of some form . . . of
sampling for integrated coverage measurement'' (pp. 2-3). Based on
the performance of DSE versus CensusPlus in the 1995 Census Test,
the Census Bureau selected the former methodology for Census 2000,
and the Panel supported that decision (White and Rust, Preparing for
the 2000 Census: Interim Report II, 51-59).
---------------------------------------------------------------------------
Also in that year, the Panel on Census Requirements in the Year
2000 and Beyond issued its final report. The Panel recommended the use
of sampling and estimation techniques in Census 2000, concluding that:
It is fruitless to continue trying to count every last person
with traditional census methods of physical enumeration * * *. It is
possible to improve the accuracy of the census count with respect to
its most important attributes by supplementing a reduced intensity
of traditional enumeration with statistical estimates of the number
and characteristics of those not directly enumerated.\48\
---------------------------------------------------------------------------
\48\ Edmonston and Schultze, Modernizing the U.S. Census, 3.
The Census 2000 Dress Rehearsal
The Census Bureau conducted a dress rehearsal in 1998 in several
sites across the country, an important opportunity to test the DSE
methodology in as near a census-like environment as possible. The
Census Bureau concluded from the dress rehearsal results that ``[t]he
data showed across-the-board that the undercount, which has been
measured in every census since 1940, persists today, but that
scientific methods used at two of the three test sites corrected for
it.'' \49\ The dress rehearsal data also displayed the persistence of
the differential undercount.\50\ In Sacramento, the estimated
undercount rates that would have resulted without the use of Integrated
Coverage Measurement were 4.7 percent for non-Hispanic Whites, compared
to 8.7 percent for African Americans, 8.3 percent for Hispanics, and
6.0 percent for Asians. In Menominee County, Wisconsin, which is
largely composed of the Menominee American Indian Reservation, the
estimated undercount rate for non-Hispanic American Indians that would
have resulted without the use of Integrated Coverage Measurement was
4.1 percent. In the South Carolina site, the estimated undercount rate
for non-Hispanic Whites was 6.3 percent and 13.2 percent for all others
(Hispanic, Black, American Indian, Hawaiian, and Asian).
---------------------------------------------------------------------------
\49\ Department of Commerce, ``Census 2000 Dress Rehearsal Shows
Undercount Persists; Scientific Methods Correct Race and Ethnic
Differential,'' Commerce News, 20 April 1999, CB99-CN.16 (revised).
\50\ Bureau of the Census, ``Some Results from the Census 2000
Dress Rehearsal,'' by Rajendra Singh, DSSD Census 2000 Dress
Rehearsal Memorandum Series A-76, 26 February 1999, 6.
---------------------------------------------------------------------------
It is clear from these results that, based on traditional census-
taking methods alone, there was a substantial net undercount in all
three sites, as well as a differential undercount of racial and ethnic
minorities in those jurisdictions. The dress rehearsal demonstrated the
operational feasibility of the A.C.E. and enhanced the Census Bureau's
knowledge of the properties of statistical correction.
External Review
The Census Bureau's confidence that the application of the DSE
methodology will result in a more accurate census is shared by many
other entities that have critically examined this issue. Four different
NAS panels over the decade have clearly endorsed the concept that a
properly designed and executed coverage measurement survey has the
potential to produce a more accurate census.\51\ In 1999, the NAS Panel
to Evaluate Alternative Census Methodologies concluded that:
---------------------------------------------------------------------------
\51\ A fourth NAS panel was convened in June 1998 to review the
Census Bureau's plans, procedures, and operations in connection with
the Dress Rehearal and Census 2000. Experts from this panel are
examining, among other things, the statistical methodology and
procedures for the A.C.E.
The only cost-effective methodology available for measuring the
degree of differential undercoverage for subnational areas is a
large-scale post-enumeration survey coupled with dual-system
estimation * * *. If the Supreme Court prohibits use of integrated
coverage measurement for apportionment, the panel still strongly
supports a post-enumeration survey * * * for purposes other than
apportionment.\52\
---------------------------------------------------------------------------
\52\ Cohen, White, and Rust, Measuring a Changing Nation, 4.
This recent conclusion is in line with those of the other three NAS
panels. For example, in 1995, the Panel on Census Requirements in the
Year 2000 and Beyond concluded that use of a high-quality survey in
conjunction with the 2000 census will result in ``* * * improved
accuracy with respect to the count and differential undercount for the
nation as a whole as well as large areas and groups.'' \53\
---------------------------------------------------------------------------
\53\ Edmonston and Schultze, Modernizing the U.S. Census, 100.
---------------------------------------------------------------------------
Numerous other organizations agree that the use of a properly
conducted scientific survey in conjunction with the enumeration has the
potential to produce a more accurate census in 2000.\54\ These include,
among others, the American Statistical Association, the American
Sociological Association, the General Accounting Office, the Inspector
General of the Department of Commerce, the Secretary of Commerce's
Census 2000 Advisory Committee, the Census Bureau's Advisory Committee
of Professional Associations, and the Census Bureau's Race and Ethnic
Advisory Committees.\55\
---------------------------------------------------------------------------
\54\ While support is widespread, the Census Bureau does not
mean to imply that there is unanimous support on the issue. See, for
example, Lawrence D. Brown and others, ``Statistical Controversies
in Census 2000,'' Jurimetrics 39 (Summer 1999).
\55\ Bureau of the Census, ``Report to Congress--The Plan for
Census 2000,'' 24-25; Joint Census Advisory Committees on the Racial
and Ethnic Populations, ``Recommendations Agreed Upon by the Four
Census Advisory Committees on the African American, American Indian
and Alaska Native, Asian and Pacific Islander and Hispanic
Populations Made at the Meeting Held on May 22-23, 1997,''
Recommendation 3; the Secretary of Commerce's 2000 Census Advisory
Committee, ``Final Report, Recommendation 3B, Post Enumeration
Survey with a Traditional Census,'' 22 January 1999; and Census
Advisory Committee of Professional Associations, ``Recommendations
Made as a Result of the Meeting on April 22-23, 1999,''
Recommendation 1.
---------------------------------------------------------------------------
A.C.E. Implementation Issues
The 1990 census coverage measurement survey was one of the most
thoroughly evaluated programs conducted by the Census Bureau. The
Census Bureau and other interested parties have analyzed volumes of
data on the survey's effects on accuracy and how its results compared
to the 1990 unadjusted census. Some of this analysis was performed in
conjunction with Secretary Mosbacher's 1991 decision and the 1992
Committee on
[[Page 38386]]
Adjustment of Postcensal Estimates (CAPE) report, but the Census Bureau
has continued to examine the adjusted and unadjusted census data from
1990. These analyses have further clarified the relationship between
the adjusted and the unadjusted 1990 census counts.
The extensive study of the 1990 coverage measurement survey
identified a number of issues. The Census Bureau has considered these
and other issues in assessing the feasibility of statistically
correcting the Census 2000 counts. The following discussion presents
many of these issues and addresses why the Census Bureau expects the
A.C.E. to improve the overall accuracy of the census. In addition,
changes in the A.C.E. design and their impact on accuracy are
discussed.
Measuring Accuracy
Measuring accuracy in both the enumeration and the coverage
measurement survey involves examining two types of error. One type,
sampling error or variance, arises from the use of a sample to
represent a population. Sampling error will occur only in the A.C.E.
The other type, often termed nonsampling error, represents all other
sources of error. Of particular concern in nonsampling errors are
systematic errors or biases. Nonsampling errors will occur in both the
initial census and the A.C.E. The most serious source of bias in the
initial census is coverage error resulting from people missed or
erroneous enumerations. The most notable example of bias in the
enumeration is the historical phenomenon of the net undercount,
including the differential undercount. Bias can also occur in the
A.C.E., including errors due to false matches or nonmatches,
inaccurately accounting for missing information, and other systematic
collection or processing errors.
In designing coverage measurement surveys, the Census Bureau must
strike a balance between sampling variance and bias. In comparing the
accuracy of the 1990 coverage measurement survey to the accuracy of the
unadjusted census, the Census Bureau concluded that the combined error
in the coverage measurement survey was lower than the large bias in the
census enumeration and therefore recommended adjustment. Secretary
Mosbacher did not accept this recommendation and explained his reasons
for not adjusting in his 1991 decision paper.
Assessment of Issues Emerging from 1990
The scrutiny and analysis of the 1990 census adjustment decision
extended and sharpened discussions in the statistical community
regarding the use of a coverage measurement survey to correct for
census undercounts. Many of these issues were the subject of extensive
discussion in Secretary Mosbacher's July 1991 decision document and in
the 1992 CAPE report. Over the past decade, issues regarding the use of
sampling to correct the census have been debated frequently in the
technical literature.\56\
---------------------------------------------------------------------------
\56\ Wright and Farmer, ``A Bibliography of Selected Statistical
Methods Related to Census 2000.''
---------------------------------------------------------------------------
Some of these issues primarily address the basic principles and
theories that must be considered in determining the proper application
of a coverage measurement survey and DSE. For these issues reasoned
judgment has to be invoked, and it is difficult to resolve these issues
definitively by quantitative measurements. For example, what is the
proper standard for deciding whether the coverage measurement survey
should be used to correct the census? What priority should be given to
numeric versus distributive accuracy? What are plausible assumptions
about the distribution of individuals who are missed by both the
initial census and the coverage measurement survey?
Other issues focus more on how well the Census Bureau can implement
the coverage measurement survey, including the estimation processes. Is
it operationally feasible to conduct the A.C.E. and produce the
corrected results within the decennial time frame? Are the levels of
sampling variance associated with the A.C.E. estimates reasonable? Can
the levels of matching or other processing errors that occur in A.C.E.
operations be kept to a minimum? These issues, while still subject to
some degree of technical judgement, can often be evaluated by an
examination of quantitative data.
As part of its comprehensive assessment of the A.C.E. design,
senior Census Bureau officials requested a careful analysis of the
technical issues identified in both the Mosbacher document and the CAPE
report in order to ensure that cited concerns about accuracy had been
adequately addressed. The Census Bureau's analysis of the Mosbacher
document focused on the Secretary's guidelines and on supporting
evidence for his decision.\57\ The Census Bureau's analyses of the CAPE
report focused on the accuracy of the unadjusted versus the adjusted
census counts for different levels of geography and the status of the
technical issues introduced.\58\
---------------------------------------------------------------------------
\57\ Bureau of the Census, ``An Analysis of the Consistency of
the 1990 Mosbacher Guidelines to U.S. Census Bureau Standards,'' by
Sally M. Obenski and Robert E. Fay, 16 May 2000.
\58\ Obenski and Fay, ``Analysis of CAPE Findings on PES
Accuracy''; and Bureau of the Census, ``Analysis of CAPE Findings on
1990 PES Technical Issues,'' by Sally M. Obenski, 9 June 2000.
---------------------------------------------------------------------------
In addition to the discussion of technical issues, Secretary
Mosbacher's analysis (and other reports critical of sampling)
introduced a number of non-technical considerations. Secretary
Mosbacher, for example, opined that ``adjustment would open the door to
political tampering with the census in the future'' \59\--a theme
frequently repeated in political, though not in scientific, discussions
of sampling. No evidence has been presented that the Census Bureau has
the competence to assess how its selection or implementation of census
operations, including the many technical components of the A.C.E.,
might predetermine partisan outcomes. Furthermore, the highly pre-
specified A.C.E. procedures make Census 2000 highly resistant to any
form of manipulation. Although there are a number of agencies and
groups--including the congressional committees charged with oversight
of Census 2000, the General Accounting Office, the Census Monitoring
Board, the Inspector General of the Department of Commerce, numerous
advisory committees and other watchdog efforts--scrutinizing the
planning and conduct of Census 2000, no evidence has been presented
suggesting that the Census Bureau has any intention to affect political
outcomes, or, if it did, that it has the technical ability to do so.
The Census Bureau disputes any and all accusations that it would act
out of political motives, and in this document restricts its discussion
of concerns about the A.C.E. to those with technical and scientific
content.
---------------------------------------------------------------------------
\59\ Department of Commerce, ``Adjustment of the 1990 Census,''
33583.
---------------------------------------------------------------------------
The Proper Standard To Use in Deciding Whether to Statistically Correct
the Counts for Non-Apportionment Purposes
As was discussed earlier, Secretary Mosbacher's adjustment decision
regarding the 1990 census was controlled by eight guidelines
promulgated in connection with pending litigation. Secretary
Mosbacher's decision not to adjust the 1990 census was based in large
part on the standard articulated in the first guideline--that the
unadjusted census would be ``* * * considered the most accurate count
of the population of the United States, at the national, state, and
[[Page 38387]]
local level, unless an adjusted count is shown to be more accurate.''
Analysis and Response
This guideline assumed a priori that the unadjusted census counts
were superior and required proof that the adjusted counts were better
in terms of distributive accuracy at all three levels. This decision
guideline required the adjusted counts to satisfy criteria that no
other census operation could meet--in effect, the 1990 census coverage
measurement survey was subjected to a higher standard than all other
census operations.
If the Census Bureau had historically applied a similar presumption
that a change to the census operation must demonstrate increased
accuracy with convincing evidence for small levels of geography, it
would not have made many important changes in census-taking
methodology. For example, such a standard would not have permitted the
Census Bureau to replace 100-percent in-home ``personal'' visits with
mail questionnaires in the 1970 census. The Census Bureau did not know
whether this fundamental change to the census operation would increase
accuracy at all levels. Nor, in 2000, could the Census Bureau determine
a priori that extensive promotion and paid advertising would increase
accuracy at all levels, or for that matter, would be effective in all
areas or for all demographic groups. If applied to all proposals to
improve the initial census counts, this standard would effectively halt
the Census Bureau's long tradition of scientific and technical
innovation.
For Census 2000, the Census Bureau will make the determination on
whether to use the A.C.E. to correct Census 2000 after evaluating (1)
the conduct of key operations, (2) the consistency of the A.C.E.
results with historical measures of undercount, and (3) measures of
quality. As described previously, the Census Bureau's comprehensive
ongoing analyses and experience with conducting coverage measurement
surveys have led it to expect that the A.C.E. will improve overall
numeric and distributive accuracy and that it will reduce the
differential undercount. Therefore, statistical correction is
appropriate absent strong evidence that it will degrade the overall
quality of the final census data. However, the Census Bureau will
conduct an objective review before making a final determination to
release the statistically corrected data. The process that the Census
Bureau will follow in making this determination is described in more
detail at the end of this document. The Census Bureau will be
documenting and discussing both this process and the criteria on which
the determination will be made in a public setting in the fall of 2000.
Numeric v. Distributive Accuracy
The 1990 census adjustment decision (and the closely related
decision on the adjustment of the postcensal estimates) was unequivocal
in giving priority to distributive over numeric accuracy. Secretary
Mosbacher interpreted the Constitutional and legal purposes of the
census to require that:
* * * accuracy should be defined predominately in terms of getting
the proportional distribution of the population right among
geographic and political units. This argues for putting aside the
judgment of accuracy based on getting absolute numbers right
(numeric accuracy) and instead focusing on the question of whether
there is convincing evidence that the accuracy of population
distribution in the adjusted numbers (distributive accuracy) is
superior to the distributive accuracy of the actual enumeration.\60\
---------------------------------------------------------------------------
\60\ Ibid., 33593.
This injunction, when joined with the standard in the first
guideline, requires not only that the adjusted counts be demonstrably
more accurate at very low levels of geography but that they be more
distributively accurate at those levels. This emphasis was reflected in
many of the technical papers that have been written on the 1990 census.
Comparatively less attention has been directed to the importance of
numeric accuracy, despite the importance that the Census Bureau
attaches to it. In fact, Secretary Mosbacher critiqued the Census
Bureau for its interpretation ``of accuracy as concerned with getting
the number of people closer to the truth rather than getting the
allocation of the population for the purposes of political
representation and funding closer to the truth.'' \61\
---------------------------------------------------------------------------
\61\ Ibid., 33592.
---------------------------------------------------------------------------
Analysis and Response
The Census Bureau believes that the adjustment decision in 1990 did
not adequately consider the improvements to numeric accuracy that can
result from statistical correction. Numeric and distributive accuracy
are discussed more fully above. The issue here is the relative
importance that should be assigned to numeric and distributive accuracy
in assessing the results of the coverage measurement survey. Judgments
can differ on this issue. It is the strong judgment of the Census
Bureau that in deciding whether to use a coverage measurement survey to
improve the census, both numeric and distributive accuracy should be
taken into account.
The analysis and decision in 1990 focused almost exclusively on
distributive accuracy. Although Secretary Mosbacher stated that the
Census Bureau had provided substantial evidence (although ``not
necessarily convincing'') that the adjusted counts were more
numerically accurate, he based his conclusion not to adjust partially
on the fact that improvements to distributive accuracy could not be
demonstrated by convincing evidence at national, state, and local
levels.\62\ Given the decision criteria introduced by Secretary
Mosbacher, the CAPE also focused on distributive accuracy.
---------------------------------------------------------------------------
\62\ Ibid., 33584.
---------------------------------------------------------------------------
The interaction between numeric and distributive accuracy is quite
complicated, but must be considered in the analysis of the two types of
accuracy. Clearly, there are situations where gains in numeric accuracy
are expected without improvement in distributive accuracy. For areas or
groups that have similar undercount rates, improvements to numeric
accuracy are expected from the A.C.E. corrections. However, the
distributive accuracy of these areas will be unchanged by the
correction, because they will experience similar corrections. This
outcome is expected, because gains in distributive accuracy are
realized when areas corrected for significant undercounts are compared
with areas that have little undercount. Because the A.C.E. is designed
to improve the numeric accuracy of areas with significant undercounts,
the Census Bureau expects that the A.C.E. will improve both numeric and
distributive accuracy and thus result in a more accurate census
overall.
Correlation Bias
Correlation bias is the result of either lack of independence
between the initial census and the coverage measurement survey, or of
variable inclusion probabilities within a post-stratum.\63\ Frequently,
the term is used to refer to error caused by individuals systematically
missed in both the initial census and the coverage measurement survey.
Important assumptions for DSE are that everyone in a given post-stratum
has a similar inclusion probability and that the census and the
coverage measurement survey are independent. Technically, these
assumptions are referred to as homogeneity and causal independence,
respectively. Correlation bias occurs when these assumptions are not
fully satisfied. Although it is theoretically possible for correlation
bias to result in
[[Page 38388]]
either underestimation or overestimation by DSE, it is generally
expected that correlation bias leads to underestimation. This will be
the case, for example, when there are individuals who have little or no
chance of being included in either the initial census or the coverage
measurement survey. Some critics of the 1990 coverage measurement
survey were concerned that correlation bias was so large as to preclude
an improvement in distributive accuracy from adjustment.\64\
---------------------------------------------------------------------------
\63\ CAPE, 21-23.
\64\ Department of Commerce, ``Adjustment of the 1990 Census,''
33591-92.
---------------------------------------------------------------------------
Analysis and Response
Correlation bias exists and will affect all dual system estimates.
Post-stratification is used to minimize correlation bias. However,
post-stratification is not a perfect solution, and it is reasonable to
presume that some heterogeneity or causal dependence will persist,
leading to some correlation bias. Comparisons with Demographic
Analysis, though subject to limitations, have been used to obtain
indications of possible correlation bias at the national level by age-
sex-race groups. These comparisons in 1990 suggested correlation bias
for adult Black males, and gave much less or no evidence of correlation
bias for other groups. These analyses were restricted to the national
level, and gave no indication of how any persons reflected in
correlation bias may have been distributed geographically. In fact,
there are no empirical data that can be used to definitely measure
correlation bias below the national level. As a result, different
hypotheses have been set forth regarding whether the A.C.E. will
improve accuracy, particularly distributive accuracy. In the absence of
quantitative data, the issues regarding the effects of correlation bias
can only be resolved by a review of the assumptions underlying the
various hypotheses, and by making judgments regarding which assumptions
are more plausible.
The uncertainty about the geographic distribution of persons
reflected in correlation bias relates to a concern of Secretary
Mosbacher--the concern that because the distribution of those people
missed by both the census and the coverage survey was not known, it
could not be demonstrated that a statistical correction would improve
distributive accuracy.\65\ However, such a concern implicitly assumes
that the distribution of correlation bias in dual system estimates
differs from the distribution of undercount, as estimated in A.C.E.
While recognizing the inherent limitations of its knowledge about the
distribution of correlation bias, the Census Bureau believes it is more
plausible to assume that correlation bias will tend to be distributed
in a positive relation to the distribution of estimated undercount
rates. A range of models reflecting plausible assumptions for the
distribution of correlation bias have been analyzed.\66\ This analysis
of correlation bias, based on plausible assumptions, leads the Census
Bureau to expect that improvements in distributive accuracy will be
achieved by a properly designed and conducted coverage measurement
survey.
---------------------------------------------------------------------------
\65\ Ibid.
\66\ William R. Bell, ``Using Information from Demographic
Analysis in Post-Enumeration Survey Estimation,'' Journal of the
American Statistical Association 88 (September 1993): 1106-1118; and
Bureau of the Census, ``Report of the Working Group on the Use of
Demographic Analysis in Census 2000,'' by William R. Bell and
others, 6 May 1996.
---------------------------------------------------------------------------
Potential effects of correlation bias on numeric accuracy can also
be addressed. Correlation bias, when present, is generally expected to
lead to underestimation by dual system estimates. Therefore, when the
DSE estimates an undercount in the initial census, by implication the
initial census counts are even more severely undercounted. So the
statistical corrections based on DSE are moving the census counts in
the right direction, though not far enough. Thus, the statistical
correction improves numeric accuracy when the groups subject to
correlation bias are also undercounted by the census. In fact, the
group identified by Demographic Analysis as probably subject to
significant correlation bias in 1990 `` adult Black males `` also had a
high estimated undercount rate from the 1990 PES.\67\
---------------------------------------------------------------------------
\67\ CAPE, Table 2, Attachment 3A.
---------------------------------------------------------------------------
The Census Bureau expects that a properly designed and conducted
coverage measurement survey should improve both numeric and
distributive accuracy, even accepting that correlation bias cannot be
eliminated. The Census Bureau will continue to use Demographic Analysis
to assess the possibility of correlation bias at the national level.
Accuracy at Different Geographic Levels
When Secretary Mosbacher decided not to use the adjusted data in
1991, he indicated that the adjusted data could not be shown by
convincing evidence to be more distributively accurate at the national,
state, and local levels. The June 1991 Undercount Steering Committee
report and later the August 1992 CAPE report concluded that adjustment,
on average, improved distributive accuracy for states and areas with
populations of more than 100,000.\68\ The CAPE report, however, left
the erroneous impression that the unadjusted census was more accurate
at small geographic areas, generally, areas with a population of fewer
than 100,000.
---------------------------------------------------------------------------
\68\ Bureau of the Census, ``Technical Assessment of the
Accuracy of Unadjusted Versus Adjusted 1990 Census Counts,'' Report
of the Undercount Steering Committee, 21 June 1991, p. 2; and CAPE,
1.
---------------------------------------------------------------------------
Analysis and Response
The CAPE report, issued on August 7, 1992, was followed by a
November 25, 1992, Addendum. Because the CAPE work was conducted at the
request of Secretary Mosbacher, the committee implicitly adopted the
framework of the Mosbacher adjustment decision process in reaching its
conclusions. That is, the adjusted census counts had to be shown to be
more accurate at state and local levels in order to be adopted. The
committee determined that it was unable to show that the adjusted
census counts were more distributively accurate than the unadjusted
counts for areas with fewer than 100,000 in population. Accordingly,
the CAPE concluded that the unadjusted counts should be used in the
postcensal estimates program. Unfortunately, the initial CAPE report
could be interpreted as indicating that there was a problem with the
accuracy of the adjusted census numbers for areas with a population of
fewer than 100,000.
It is important to understand, however, that the Census Bureau did
not stop its research into small area accuracy with the initial CAPE
report. The initial CAPE analysis reported the Census Bureau's results
from its first comparisons, comparisons of similar areas. For example,
areas with populations of fewer than 25,000 were compared to each
other, and major metropolitan areas were compared to each other. But
the Census Bureau conducted additional research, comparing large cities
and counties to each other, to the balance of the nation, and to the
balance of their respective states. This additional research reported
in the Addendum documented additional evidence of improvements in
distributive accuracy at sub-state levels.\69\
---------------------------------------------------------------------------
\69\ CAPE Addendum.
---------------------------------------------------------------------------
The correct interpretation of the CAPE report and the Addendum is
that the Census Bureau could distinguish no improvement in distributive
sub-state accuracy if the corrected numbers had been used to produce
estimates for areas
[[Page 38389]]
with populations of less than 100,000. It is incorrect to infer that
the unadjusted census produced more distributively accurate sub-state
data. That question was not tested in the CAPE research.
More recently, the Census Bureau has re-examined the CAPE data and
determined that, based on available data, there is no basis for
concluding that the unadjusted census was more distributively accurate
than the adjusted counts for small areas.\70\ That is, in general, no
differences in the distributive accuracy of these two sets of counts
have been demonstrated for geographic areas with less than 100,000
population.
---------------------------------------------------------------------------
\70\ Obenski and Fay, ``Analysis of CAPE Findings on PES
Accuracy.''
---------------------------------------------------------------------------
Based on the CAPE and subsequent research and the expectation that
the error structures of the initial census and A.C.E. operations for
Census 2000 will be similar to 1990, the Census Bureau expects that the
A.C.E. will, on average, increase distributive accuracy for areas with
100,000 or more residents. For areas with fewer than 100,000 people,
the predicted effect of the A.C.E. on distributive accuracy is
indeterminate--neither favoring the initial census nor the corrected
counts.
With respect to numeric accuracy, as noted above, the Census Bureau
expects that the A.C.E. will, on average, improve accuracy for
geographic areas down to and including census tracts. Furthermore, the
Census Bureau expects that improvement will be greatest for those areas
that contain groups that have been historically undercounted.
Consistency with Demographic Analysis
The analysis of the 1990 coverage measurement survey included a
comparison of the adjusted census with estimates based on Demographic
Analysis (DA).\71\ Discrepancies between the adjusted census and DA
estimates led Secretary Mosbacher and others to question the accuracy
of the 1990 adjusted census counts.
---------------------------------------------------------------------------
\71\ Bell, ``Using Information from Demographic Analysis in
Post-Enumeration Survey Estimation,'' 1106-1118; and Robinson and
others, ``Estimates of Population Coverage in the 1990 United States
Census,'' 1061-77.
---------------------------------------------------------------------------
Analysis and Response
Demographic Analysis uses records and estimates of births, deaths,
immigration, Medicare enrollments and estimates of emigration and
undocumented immigration to estimate the national population,
separately from the census. These demographic benchmarks are compared
to the census counts, and the differences are used to create an
estimate of the net census undercount. These estimates are produced for
age groups (single years of age), sex, and broad race groups (Black,
Non-Black). DA estimates can be used as independent benchmarks to
validate the accuracy of coverage measurement survey estimates for
corresponding demographic categories.
It is important to note that DA, like coverage measurement surveys,
has an associated level of uncertainty. The Census Bureau developed
quantitative measures of uncertainty for the 1990 DA estimates, but
these measures are based in part on professional judgment about the
range of error in each of the underlying demographic components.
How much uncertainty to assign to a DA estimate is therefore a
matter of judgment. Different conclusions will be reached depending on
basic assumptions about the accuracy of vital statistics and other
records used in DA. In 1990, the Undercount Steering Committee
concluded that the uncertainty in the DA estimates was of a magnitude
that meant that many of the differences with the coverage measurement
survey estimates resulted from random variation. However, Secretary
Mosbacher reached another conclusion, citing several ``important and
puzzling differences'' between the survey estimates and the DA
estimates.\72\ The Census Bureau, based on previous work in this area,
concluded that some noted differences were expected, but these
differences did not call into question the results of the coverage
measurement survey.\73\ Indeed, the difference between the DA and 1990
PES estimates for adult Black males was beyond the bounds of
uncertainty, demonstrating the utility of Demographic Analysis for
assessing correlation bias at the national level. Other differences
fell within acceptable bounds of uncertainty associated with both sets
of estimates. The Census Bureau considered all differences between the
DA estimates and coverage measurement survey estimates in its
determination that the coverage measurement survey did improve the
accuracy of the census counts. For Census 2000, the Census Bureau will
continue to compare both the uncorrected and corrected census counts
with DA estimates.
---------------------------------------------------------------------------
\72\ Department of Commerce, ``Adjustment of the 1990 Census,''
33587.
\73\ Bureau of the Census, ``Technical Assessment of the
Accuracy of Unadjusted Versus Adjusted 1990 Census Counts,'' 4.
---------------------------------------------------------------------------
Timing
In 1990, the adjusted data were not available for release until
July 1991. This raises a concern about whether the Census Bureau can
produce the statistically corrected data within the statutory deadline
of April 1, 2001, for redistricting, without sacrificing the quality of
the initial census or the A.C.E.
Analysis and Response
The timing and quality of the initial census and the A.C.E. are
related. The Census Bureau has developed a schedule for the initial
census and for the A.C.E. operations that allows adequate time to
produce uncorrected data for apportionment and corrected data prior to
the statutory deadline. Barring some major, unanticipated operational
difficulty,\74\ the Census Bureau expects to complete all data
collection and processing functions for the initial census and the
A.C.E. in time to deliver quality, statistically corrected
redistricting numbers to the states prior to April 1, 2001.
---------------------------------------------------------------------------
\74\ Census Bureau Director Dr. Prewitt provided examples of
such operational difficulties in his February 14, 2000, letter to
Chairman Dan Miller of the House Subcommittee on the Census. These
examples include: (1) Problems with the payroll system that prevent
the Census Bureau from paying its employees on a timely basis; (2)
widespread problems filling enumerator positions, despite the
agency's extensive pool of qualified applicants; and (3) problems
with the Census 2000 address file that prevent Census Bureau
employees from being able to fulfill their responsibilities.
---------------------------------------------------------------------------
Critical differences between the 1990 census and plans for Census
2000 should allow production of the corrected numbers within the
required period. First, the 1990 plan was not premised on producing the
adjusted numbers by the April 1 deadline. In fact, the 1990 litigation
established a deadline of July 15, 1991, for delivery of the adjusted
data.
Second, there are improvements to the census that will make the
initial Census 2000 operations more timely. While these improvements
are directed at allowing enumeration data collection to occur closer to
Census Day and therefore to be more accurate, they will also allow for
an earlier start for the A.C.E. With respect to the key issue of
staffing nonresponse followup so as to finish on schedule, which is
crucial to the progress of both the census and the A.C.E., the Census
Bureau has developed strategies to avoid the recruitment and retention
problems that extended the 1990 census NRFU operation. The Census
Bureau has conducted extensive research on how to ensure the
recruitment and retention of well-qualified temporary employees. These
strategies, successfully employed during the Census 2000 dress
rehearsal, included the targeting of wage rates to local areas and a
technique called frontloading. Frontloading is directed at
[[Page 38390]]
reducing the effects of early turnover of employees by hiring two
employees for every position. As a result of these and other changes,
nonresponse followup will take place in a shorter time period in Census
2000. This shortening of nonresponse followup is in accord with the
observations of the Census Bureau and the General Accounting Office
that NRFU results decrease in accuracy as the time from Census Day
increases.\75\ In addition, Census 2000 will not be repeating certain
ineffective coverage improvement programs that delayed processing of
the initial census in the 1990 coverage measurement survey.\76\
---------------------------------------------------------------------------
\75\ Bureau of the Census, ``Characteristics of Census Errors,''
by Deborah Griffin and Christopher Moriarity, 1990 Decennial Census
Preliminary Research and Evaluation Memorandum No. 179, 15 September
1992; and General Accounting Office, Decennial Census--1990 Results,
47.
\76\ These coverage improvement programs are discussed briefly
in Cohen, White, and Rust, Measuring a Changing Nation, 32-33.
robop...@us.govnews.org
Posting-number: Volume 65, Issue 119, Page 38373, Part 1
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Third, several important changes will improve the timeliness of the
A.C.E. operation. For example, the A.C.E. interviewers will have
received more extensive training than in 1990. Additionally, the Census
Bureau has developed a Computer Assisted Person Interviewing (CAPI)
system for the A.C.E. that will allow enumerators to collect the data
more quickly and accurately, and to transmit it electronically in a
more expeditious manner by using laptop computers.
In the unlikely event of an unanticipated, major operational
difficulty, the Census Bureau will not curtail important operations key
to the quality of the entire census to stay on schedule. For example,
the Census Bureau will not curtail nonresponse followup in difficult-
to-enumerate neighborhoods to stay on the A.C.E. schedule. Likewise,
the Census Bureau will not curtail the A.C.E. data collection
activities. The Bureau is committed to achieving high quality in all
census operations, and Census Bureau statisticians will be monitoring
key A.C.E. performance information, such as response rates, for early
warning about areas warranting corrective actions.
Level of Sampling Variance/Smoothing
The levels of sampling variance and bias in the 1990 coverage
measurement survey were important topics in the adjustment debate.
Sampling variance is discussed in this section; bias will be discussed
in the following section.
Analysis and Response
One issue in 1990 was the use of a statistical technique called
smoothing, a complex, model-based method designed to control sampling
variance. The use of smoothing led to an extensive discussion regarding
the robustness of the 1990 methodology. For Census 2000, the Census
Bureau has developed the A.C.E. sample design so that smoothing will
not be necessary. There were also concerns about the overall level of
sampling variance in the 1990 coverage measurement survey.\77\ In
developing the A.C.E. design, the Census Bureau thoroughly examined
1990 variance issues and made important design decisions to reduce
sampling variance levels. These include:
---------------------------------------------------------------------------
\77\ Bureau of the Census, ``Adjustment of the 1990 Census,''
passim.
---------------------------------------------------------------------------
<bullet> The A.C.E. sample size is almost double that of 1990,
increased from approximately 165,000 to 314,000 housing units. Because
sampling variance is inversely proportional to sample size, this
increase will reduce the level of sampling variance in 2000.
<bullet> The A.C.E. sample was designed to minimize the range in
size of the sampling weights. Weights are assigned to categories of
blocks (that is, small and large) that have different probabilities of
being selected in the sample. When there is a wide range of weights,
variance increases because blocks with large weights have a
disproportionate effect on the variance of the estimates. The Census
Bureau has designed its sampling procedures for Census 2000
specifically to limit how much these weights will vary. This design
will result in reduced sampling variance.\78\
---------------------------------------------------------------------------
\78\ The NAS agrees that design changes in the A.C.E. will
reduce the variance in block sampling weights, a ``key improvement
in comparison to the 1990 design,'' May 3, 1999, letter from Janet
L. Norwood, Chair, NAS Panel to Review the 2000 Census, to Kenneth
Prewitt, Director, U.S. Bureau of the Census.
---------------------------------------------------------------------------
The Census Bureau has used the 1990 experience to develop an
enhanced A.C.E. sampling design, and does not anticipate that variance-
related issues will be a serious source of concern for the Census 2000
coverage measurement survey.
Level of Nonsampling Error/Bias
One concern was that the level of nonsampling error or bias in the
1990 coverage measurement survey was so large that statistical
correction would not result in an improvement in distributive
accuracy.\79\ Critics of the A.C.E. have expressed similar concern
about the anticipated level of bias in the Census 2000 DSE.\80\
---------------------------------------------------------------------------
\79\ Bureau of the Census, ``Adjustment of the 1990 Census,''
and Leo Breiman, ``The 1991 Census Adjustment: Undercount or Bad
Data?'' Statistical Science 9, no. 4 (1994): 458-537.
\80\ David A. Freedman and Kenneth Wachter, University of
California, letter to Rep. Miller, Chairman, House Subcommittee on
the Census, 17 May 2000; and Brown and others, ``Statistical
Controversies in Census 2000.''
---------------------------------------------------------------------------
Analysis and Response
The Census Bureau conducted extensive evaluations of nonsampling
error in the 1990 coverage measurement survey.\81\ These evaluations
have given the Census Bureau a detailed understanding of nonsampling
error. Based on this extensive work, the Census Bureau has concluded
that the levels of nonsampling error in the 1990 PES did not prevent
the statistical correction based on the coverage measurement survey
from improving the accuracy of the census counts.\82\ The A.C.E. design
includes enhancements to the 1990 coverage measurement survey that will
even further control nonsampling error.
---------------------------------------------------------------------------
\81\ Bureau of the Census, ``Technical Assessment of the
Accuracy of 1990 Census Counts,''4; and Mary H. Mulry and Bruce D.
Spencer, ``Accuracy of the 1990 Census and Undercount Adjustments,''
Journal of the American Statistical Association 88 (September 1993):
1080.
\82\ Bureau of the Census, ``Technical Assessment of the
Accuracy of 1990 Census Counts,'' 1.
---------------------------------------------------------------------------
It is important to note that some amount of bias in both the
initial census and the A.C.E. is inevitable. However, the Census
Bureau's analysis of bias, grounded in sound statistical principles,
leads to the expectation that the improvements described in the
following sections will control the levels of nonsampling error in the
A.C.E. so that a statistical correction based on the A.C.E. will
improve the uncorrected counts.
Enhancements to the Matching Process
Matching refers to the determination of whether an individual
enumerated in a coverage measurement survey is the same person as an
individual enumerated in the initial census operation. Because errors
in matching can significantly affect undercount estimates, highly
accurate matching is an important component of the A.C.E. methodology.
Although neither Secretary Mosbacher nor CAPE identified matching error
as a significant problem with the 1990 coverage measurement survey, the
Census Bureau has made significant improvements to the matching process
in the 2000 A.C.E. design, and matching error is expected to be even
lower in Census 2000 than in 1990:
<bullet> A fully automated system supports computer and clerical
matching, an advance over 1990 procedures that required handling and
control of paper documents. This improvement provides for a number of
built-in edits and quality checks to control matching error.
[[Page 38391]]
The automated matching system is the culmination of Census Bureau
analyses and refinements over the last 20 years and will make searching
and matching easier and more reliable.
<bullet> The matching processes have been centralized in one site,
rather than decentralized as in 1990, allowing for more effective
control--a well-trained staff will perform all matching at a single
location.
<bullet> As discussed below, the change in the treatment of people
who have moved since Census Day will simplify matching for these
movers. Unlike in 1990, it will only be necessary to match people who
resided in the sample blocks on April 1.
Enhancements to Computer Processing
After the initial release of the adjusted numbers in July 1991, the
Census Bureau discovered a computer processing error that resulted in a
0.4 percent decrease in the estimated undercount for the 1990 census.
The CAPE report reduced the Census Bureau's official undercount
estimate from 2.1 percent to 1.6 percent, with 0.4 percentage points
attributable to the computer processing error, and 0.1 percent
attributable to additional processing corrections. Concerns have been
raised relating to the Census Bureau's late discovery of the computer
processing error. These concerns have been cited as evidence that the
complexity of the computer operations associated with incorporating the
results of a coverage measurement survey--like the A.C.E.--in the
census counts makes the final numbers vulnerable to significant
processing errors.\83\
---------------------------------------------------------------------------
\83\ Congress, House, Committee on Government Reform and
Oversight, Prepared Testimony of K.W. Wachter and D.A. Freeman
Before the House Committee on Government Reform and Oversight, 104th
Cong., 1st sess., 29 February 1996.
---------------------------------------------------------------------------
The Census Bureau has adopted a number of methods to improve the
quality of the A.C.E. software to guard against a similar error in
Census 2000:
<bullet> To ensure reliability, the Census Bureau has included
software validation and verification strategies, such as independent
software development of key computer programs (double programming).
<bullet> To reduce ambiguity and increase communication, the Census
Bureau has enforced standardized nomenclature and adopted an improved
documentation approach for technical issues.
<bullet> The Census Bureau has developed a Sample Design Control
System. This system provided the necessary data to control, monitor,
and validate the different phases of sampling. It also ensured that the
software used to select the A.C.E. sample functioned correctly.
<bullet> The software programs supporting the A.C.E. estimation
process will be further validated by an Integrated Review System. This
system will provide data on all phases of the estimation process that
will allow timely validation that the software is performing as
specified.
These and other initiatives should result in a controlled, robust,
and reliable A.C.E. computer processing environment. Therefore, the
Census Bureau expects the processing for the Census 2000 A.C.E. to be
not only more streamlined but also more reliable than it was for the
1990 PES.
Enhancements to Minimize Missing Data
Missing data cases involve the following situations where complete
information cannot be obtained: missing characteristic data (race, age,
or other characteristic information), complete non-interviews, or cases
with insufficient information to determine an individual's enumeration
or match status. In 1980, missing data in the coverage measurement
survey was a serious problem and factored into senior statisticians'
conclusion that the estimates were not sufficiently reliable to use for
statistical adjustment of the census counts. The Census Bureau took
steps to minimize missing data in the 1990 coverage measurement survey,
and missing data in 1990 did not significantly affect the accuracy of
the estimates.\84\ Nonetheless, concerns remain regarding the potential
for high levels of missing data in the A.C.E.
---------------------------------------------------------------------------
\84\ Bureau of the Census, ``Non-Response in Census Coverage
Measurement Surveys and Its Impact--An Historical Review,'' by Ruth
Ann Killion, DSSD Briefs, Information, and Topics Memorandum Series
No. 44C, 17 September 1998, pp. 6-7.
---------------------------------------------------------------------------
Building on its experience from the 1990 census, the Census Bureau
has designed its field operations to minimize missing data. After the
initial A.C.E. interview attempt, the Census Bureau will allow up to
two additional weeks for attempts to revisit any nonresponding
households. This two-week period of intense followup of nonresponding
households will be conducted by the Census Bureau's best and most
experienced available A.C.E. interviewers.\85\ Finally, Census Bureau
staff will be monitoring missing data rates closely throughout the
conduct of the A.C.E.
---------------------------------------------------------------------------
\85\ This intensive field operation designed to minimize missing
data is described in Childers and Fenstermaker, ``Accuracy and
Coverage Evaluation: Overview of Design,'' 7.
---------------------------------------------------------------------------
The Census Bureau has developed additional extensive procedures to
deal with missing data. One method the Census Bureau uses to handle
missing data in both the initial census and the A.C.E. is imputation.
Imputation is an established statistical methodology that completes
missing respondent information by incorporating information provided by
other similar respondents. The imputation process for Census 2000 draws
on lessons learned in the 1990 census. Additionally, the imputation
process for Census 2000 has been simplified, which should result in the
production of more easily validated data.
While missing data were not a significant issue for the 1990
census,\86\ some concerns have been expressed regarding the accuracy
and robustness of the Census Bureau's imputation model for the 1990
coverage measure survey.\87\ However, Census Bureau statisticians and
others have conducted multiple evaluations using different
methodologies to independently validate the imputation model used in
the 1990 census.\88\ These evaluations and the improvements to missing
data procedures discussed earlier lead the Census Bureau to expect that
missing data will not be a substantial problem in the A.C.E.
---------------------------------------------------------------------------
\86\ Secretary Mosbacher stated that levels of missing data were
sufficiently low so that variation in the Census Bureau's missing
data models made no difference in the outcome of the survey, and he
concurred with the Undercount Steering Committee's judgment that the
outcome was robust (Bureau of the Census, ``Adjustment of the 1990
Census,'' 33600). The CAPE, accordingly, did not examine this issue.
\87\ Brown and others, ``Statistical Controversies in Census
2000.''
\88\ T.R. Belin and others, ``Hierarchical Logistic-Regression
Models for Imputation of Unresolved Enumeration Status in Undercount
Estimation,'' Journal of the American Statistical Association 88
(September 1993): 1149-66; and Bureau of the Census, ``Documentation
of Handling Unresolved Enumeration Status in 1990 Census/Post-
Enumeration Survey,'' by Greg Diffendal and Tom Belin, STSD
Decennial Census Memorandum Series V-98, 15 January 1991.
---------------------------------------------------------------------------
Homogeneity and the Synthetic Assumption
Generally speaking, homogeneity refers to the principle that
individuals grouped in a post-stratum have similar probabilities of
being included in the census, that is, similar coverage probabilities.
If homogeneity holds, conclusions can be drawn from a sample about
population groups or geographic areas and the initial enumeration for
these population groups or areas can be corrected with a coverage
measurement survey. The synthetic assumption states that the people in
a particular post-stratum are
[[Page 38392]]
relatively homogeneous and will generally share the same coverage
factor. There are concerns, however, that a lack of homogeneity could
lead to inaccuracies being introduced into the data for areas or
population groups within the post-stratum.\89\
---------------------------------------------------------------------------
\89\ K. Wachter and D. Freedman, ``Local Heterogeneity and
Census Adjustment for the Intercensal Base,'' Technical Report No.
381 (Berkeley, CA: University of California, Department of
Statistics, 1993); and Brown and others, ``Statistical Controversies
in Census 2000,'' 13.
---------------------------------------------------------------------------
Analysis and Response
At issue is not whether there is perfect homogeneity; at issue is
whether heterogeneity is too great to prevent an improvement from using
the A.C.E. While the degree to which the homogeneity assumption holds
is a continuing issue, the Census Bureau has made design improvements
to the A.C.E. to control heterogeneity and believes that heterogeneity
will not preclude the production of useful small area data in Census
2000.
The statistical correction that results from the A.C.E. is carried
down to census blocks by applying the coverage correction factors
within each A.C.E. post-stratum. The goal in constructing post-strata
is to form groupings of the population that capture differences in the
probabilities of being included in the census and the A.C.E.\90\ In
effect, the inclusion probabilities are more similar for individuals
within the same post-stratum than for individuals in different post-
strata. The coverage correction factors are calculated for each post-
stratum, based on a representative sample of the post-stratum, and thus
reflect the net coverage of all people within the post-stratum. This is
the underlying basis for applying this factor to the data records
within the corresponding post-stratum to produce statistically
corrected block totals which serve as the basis for Census 2000
tabulations.
---------------------------------------------------------------------------
\90\ This section presents a general discussion of the basis for
synthetic or indirect estimation. There are more complex, but less
stringent, requirements involving the relationship between census
omissions and erroneous enumerations as discussed in Howard Hogan's
paper, ``Accuracy and Coverage Evaluation: Theory and Application.''
---------------------------------------------------------------------------
The more homogeneity within a post-strata and the more differences
among post-strata, the greater the improvement from statistical
correction. In designing post-strata, it is not necessary for each
individual to have the same probability of inclusion. Since no two
individuals are perfectly alike with respect to their chances of being
included in either the initial census or the A.C.E., the goal for
defining post-strata is to form groupings of the population with
similar inclusion probabilities. That is, the goal is to form post-
strata that differentiate between groups of the population with respect
to inclusion probabilities, and with respect to net coverage in the
initial census. Some have suggested that an improvement will result
from applying Demographic Analysis-based corrections within national
post-strata consistent with DA.\91\ However, the Census Bureau expects
to achieve greater improvements by having defined post-strata that take
advantage of more local data.\92\
---------------------------------------------------------------------------
\91\ David Freedman and Kenneth Wachter, ``Planning for the
Census in the Year 2000,'' Evaluation Review, 20, (August 1996):
355-77.
\92\ Bureau of the Census, ``Accuracy and Coverage Evaluation
Survey: Final Post-stratification Plan for Dual System Estimation,''
by Richard Griffin and Dawn Haines, DSSD Census 2000 Procedures and
Operations Memorandum Series Chapter Q-24, 19 April 2000.
---------------------------------------------------------------------------
The accuracy of the estimates that result from the application of
the coverage correction factors depends on the degree to which the net
coverage for areas or groups within a post-stratum is similar to the
coverage correction factor that was developed for that post-stratum.
The coverage correction factor is measured for the post-stratum based
on a representative sample, and thus represents the net coverage for
the post-stratum. Clearly, within the post-stratum, some degree of
variation is expected from the measured coverage correction factor, and
this variation will most likely be relatively greater for small areas.
Thus, it is inevitable that the A.C.E. will result in the population in
some blocks being overestimated and the population in other blocks
being underestimated. The A.C.E. statistical correction was never
intended nor expected to produce unqualified improvement in the
smallest geographic areas, like blocks. That the A.C.E. does not
produce improvement for every single block, however, is no reason to
forego the benefits that will flow from the use of corrected census
population counts at geographic levels of significance to data users.
The Census Bureau expects that the A.C.E. estimates will produce better
data for aggregations--such as states, congressional districts,
counties, and cities--that are the basic areas for which census data
are used.
The Census 2000 A.C.E. incorporates improvements from the design
used for the 1990 coverage measurement survey that are expected to
improve the homogeneity within post-strata for Census 2000.\93\ The
Census Bureau analyzed heterogeneity as part of the 1990 CAPE process,
and has continued research for the A.C.E. post-strata.\94\ Building on
the lessons learned from 1990, the Census Bureau has developed enhanced
post-strata for Census 2000. For example, the A.C.E. post-strata
definitions include mail return rate and type of enumeration
variables.\95\
---------------------------------------------------------------------------
\93\ Ibid.
\94\ Robert E. Fay and John Thompson, ``The 1990 Post
Enumeration Survey: Statistical Lessons in Hindsight,'' in
Proceedings of the 1993 Annual Research Conference, 21-24 March
1993.
\95\ Griffin and Haines, ``Accuracy and Coverage Evaluation
Survey: Final Post-stratification Plan for Dual System Estimation.''
---------------------------------------------------------------------------
Some have cited the CAPE report as evidence that the Census Bureau
had serious concerns about heterogeneity. A reading of the entire CAPE
report, including the more technical Addendum, puts these concerns in
proper perspective. That is, the full analysis of the CAPE report
(including the Addendum) supports the expectation of the Census Bureau
that the use of the A.C.E. results will lead to improvements in the
accuracy of the Census 2000 data.
Additional Design Changes From 1990
In addition to the specific improvements discussed previously, the
Census Bureau has implemented other changes to the 1990 coverage
measurement survey design. These changes, which will improve
operational efficiency, include the use of the telephone in the A.C.E.,
and changes in the treatment of movers and the search area for
matching. The Census Bureau will also collect data on race and
ethnicity differently in Census 2000. The Census Bureau continues to
consider and examine issues relating to these changes.
Use of the Telephone in A.C.E. Interviewing
To gain efficiencies in the interviewing phase of the A.C.E.,
enumerators will conduct telephone interviews using CAPI laptop
computers for households that have returned their census questionnaires
by mail. By design, this interview will take place before or concurrent
with the initial census nonresponse followup. The interviews will be
conducted from the homes of the A.C.E. enumerators and will be
conducted only for households that mail back a questionnaire that
includes a telephone number. Furthermore, the households must be in
areas where there is negligible risk of mail delivery problems--
generally, single family housing units or large multi-unit structures
in areas with city-style mail delivery.
The Census Bureau implemented this process to enhance the
efficiency and
[[Page 38393]]
quality of the A.C.E. interview. Shortening the elapsed time from
Census Day to the A.C.E. enumeration should improve data quality. Also,
starting early in an environment that is more easily controlled should
allow the A.C.E. enumerators to gain valuable experience in conducting
interviews and in operating their laptop computers. The Census Bureau
designed this process in a fashion that should maintain the
independence between the A.C.E. and the other Census 2000 operations.
New Treatment to Account for Movers
The Census Bureau has changed its treatment of individuals whose
residence changes after Census Day. In the 1990 coverage measurement
survey, movers were sampled where they lived at the time of the PES
interview. The Census Bureau then searched the census records at the
movers' April 1 usual residence to determine if they had been correctly
enumerated in the census.\96\
---------------------------------------------------------------------------
\96\ Hogan, ``Accuracy and Coverage Evaluation Theory and
Application,'' 22.
---------------------------------------------------------------------------
In the modified procedure employed by the A.C.E., the Census Bureau
will combine information on movers from two sources to produce an
estimate of movers who are missed in Census 2000. First, an estimate of
the total number of movers will be calculated based on people who moved
into the A.C.E. sample blocks between April 1 and the time of the
A.C.E. interview. Second, the rate at which movers match to Census 2000
will be based on reconstructing the Census Day residents of the A.C.E.
sample housing units and matching these residents to the initial census
records. Reconstructing the Census Day residents will be based on proxy
interviews with the new residents or neighbors. These two estimates
will be combined to form an estimate of the movers who are missed in
Census 2000. These results are then used in the Dual System Estimation.
The Census Bureau tested the modified procedure in the dress rehearsal
and has judged this procedure to be the best blend of operational
feasibility and accuracy.\97\
---------------------------------------------------------------------------
\97\ Bureau of the Census, ``Minutes of the Executive Steering
Committee on Accuracy and Coverage Evaluation Policy (ESCAP),'' 5
January 2000.
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Search Area for Matching
The Census Bureau's search operation in the 1990 coverage
measurement survey used an extended search area in blocks adjacent to
the sample blocks.\98\ The extended search area included one ring of
adjacent blocks, or two rings of adjacent blocks in most rural areas. A
person located in either the sample or an adjacent block was labeled a
correct enumeration or match. Defining the search area in this fashion
provided significant gains in reducing sampling variance. For Census
2000, the A.C.E. search area has been designed to achieve the gains in
controlling sampling variance, while providing operational
efficiencies.
---------------------------------------------------------------------------
\98\ Hogan, ``1990 Post-Enumeration Survey,'' 1054.
---------------------------------------------------------------------------
The Census 2000 search operation uses a sampling procedure that
selects A.C.E. block clusters for an extended search. All block
clusters are selected where there is evidence that an extended search
will provide substantial information needed for the A.C.E. matching.
Additionally, a random subsample of all other clusters is selected for
the extended search.\99\ This decision was based on an analysis of the
results of the 1990 census coverage measurement survey matching that
indicated that this strategy would provide virtually the same gains in
sampling variance reduction as compared to the 1990 results.\100\
---------------------------------------------------------------------------
\99\ Childers and Fenstermaker, ``Accuracy and Coverage
Evaluation: Overview,'' 8-9; and Bureau of the Census, ``Accuracy
and Coverage Evaluation: The Design Document,'' by Danny R.
Childers, DSSD Census 2000 Procedures and Operations Memorandum
Series Chapter S-DT-01.
\100\ Bureau of the Census, ``Accuracy and Coverage Evaluation
Survey: Targeted Extended Search Plans,'' by Alfredo Navarro, DSSD
Census 2000 Procedures and Operations Memorandum Series #Q-18, 12
January 2000.
---------------------------------------------------------------------------
Reporting More Than One Race
In accordance with direction from the Office of Management and
Budget,\101\ Census 2000 will for the first time allow individuals to
report more than one racial category. This guidance from the OMB
necessitates that the A.C.E. post-strata be defined taking into account
people that report more than one race. The Census Bureau, therefore,
has defined and documented the A.C.E. post-strata to include
individuals that report more than one race.\102\ The Census Bureau will
conduct a study of the effects of multiple race reporting after
completion of the census.
---------------------------------------------------------------------------
\101\ President, Executive Office, Office of Management and
Budget, ``Revisions to the Standards for the Classification of
Federal Data on Race and Ethnicity,'' Federal Register, (30 October
1997), vol. 62, no. 210, pp. 58782-90.
\102\ The Census Bureau's plan for including individuals in the
A.C.E. post-strata who report more than one race is described in
Griffin and Haines, ``Accuracy and Coverage Evaluation Survey: Final
Post-stratification Plan for Dual System Estimation,'' 1-2.
---------------------------------------------------------------------------
Making the Final Decision
The Census Bureau expects that the A.C.E., if properly conducted,
will make the census more accurate by improving coverage and reducing
differential undercounts. The Census Bureau will not, however, release
corrected redistricting data until it has brought its technical
judgment to bear in assessing the available data to verify that its
expectations have been met. The Census Bureau will consider operational
data to validate the successful conduct of the A.C.E., assess whether
the A.C.E. measurements of undercount are consistent with historical
patterns of undercount and independent Demographic Analysis benchmarks,
and review measures of quality.
In preparing for this determination, the criteria and the process
that will be followed for the assessment of the A.C.E. results will be
shared and discussed with outside statistical experts and other
interested parties in the fall of 2000. This plan is consistent with
the principle of pre-specification adopted by the Census Bureau for the
Census 2000 A.C.E. and with its open and transparent planning and
decision processes. The extent of pre-specification already publicly
provided is very extensive.
It should be noted that all major census operations are vulnerable
to unanticipated difficulties. Such difficulties could affect
production of the apportionment counts. If, for example, a major
natural disaster were to occur in a region of the country during census
nonresponse followup, and this operation were seriously disrupted, the
Census Bureau might conclude that the apportionment count so
misrepresented the ``true'' state-by-state population distribution that
it should not be used until corrective action was taken, possibly
delaying delivery of the apportionment counts past January 1, 2001.
Unanticipated difficulties could also affect the A.C.E. The Census
Bureau would respond to any major unanticipated operational difficulty
by taking steps to conduct and complete (or repeat, as necessary) all
planned operations necessary to ensure that an accurate A.C.E. had
taken place before releasing the statistically corrected data. If the
Census Bureau determines that incorporating the results of the survey
would not improve the accuracy of the initial census counts, then the
uncorrected data would be denominated as the P.L. 94-171 file.
Secretary Mosbacher's 1991 decision document raised the specter of
``political tampering'' in any use of statistically corrected census
data. To avoid even the appearance of political manipulation, the
Census Bureau has proposed a process for verifying the agency's
expectations regarding the improvements in accuracy from the A.C.E.
Under that proposal, a committee
[[Page 38394]]
of senior Census Bureau officials responsible for resolving policy and
technical issues regarding the A.C.E. and assessing the technical
effectiveness of its operations would make a recommendation to the
Census Bureau Director regarding the use of the statistically corrected
census data. The Director would make a determination regarding the use
of the statistically corrected data, taking into consideration the
recommendation of the committee. This committee, known as the Executive
Steering Committee for A.C.E. Policy (ESCAP), was formed in late 1999
and normally meets every two weeks to discuss technical and policy
issues associated with the A.C.E. and to advise the Director on these
issues. The ESCAP is chaired by the Associate Director for Decennial
Census and includes the following other senior career staff: Deputy
Director; Principal Associate Director and Chief Financial Officer;
Principal Associate Director for Programs; Associate Director for
Methodology and Standards; Associate Director for Demographic Programs;
Assistant Director for Decennial Census; Chief, Decennial Statistical
Studies Division; Chief, Planning, Research and Evaluation Division;
Chief, Population Division; Chief, Decennial Management Division; and
Senior Mathematical Statistician. The committee will document its
discussions and decisions and will make this documentation available
along with its recommendation to the Director.
Following the release of census data, the Census Bureau will
continue its research and evaluation, budget permitting. The census is
an ongoing process, and the Census Bureau implements refinements to the
data over a 10-year period. These ongoing efforts are consistent with
good science and are fundamental to the Census Bureau's work. The fact
that further research will provide more information about the success
of census operations, including the production of the apportionment
counts and the A.C.E., does not alter the requirement to release the
statistically corrected block-level numbers by the April 1, 2001,
statutory deadline, if these data meet the Census Bureau's expectations
with regard to improvements in accuracy. Evaluations of many Census
2000 operations and results, including the A.C.E., will continue after
the release of the data; and program evaluation results will be
available for planning the 2010 census and informing the scientific and
public discourse over the intervening years.
Conclusions
The Census Bureau's mission is to produce the most accurate data
possible, taking into account the intended uses of the data. The
extensive body of research that the Census Bureau has conducted on
census undercount, including the 1990 census evaluations, has
conclusively demonstrated that traditional census methodologies will
not effectively reduce the differential undercount. The Census Bureau
has concluded that based on current state-of-the-art science, the best
method or procedure that has the potential to reduce the differential
undercount and thereby increase accuracy is the application of
scientific sampling to improve traditional census methods. This view is
widespread, though not unanimous, in the professional statistical
community.
At the present time, the Census Bureau has also concluded that it
is operationally feasible to complete the A.C.E. and produce
statistically corrected census data prior to April 1, 2001, and expects
that the corrected data will be the most accurate data available. The
Census Bureau's final decision on what data to release as the most
accurate data will not be made, however, until the Census Bureau has
had an opportunity to review the conduct of the census and the A.C.E.
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____. ``Planning for the Census in the Year 2000.'' Evaluation
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____. ``Accuracy and Coverage Evaluation: Theory and Application.''
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Panel to Review the 2000 Census. 2 February 2000.
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``Recommendations Agreed Upon by the Four Census Advisory Committees
on the African American, American Indian and Alaska Native, Asian
and Pacific Islander and Hispanic Populations Made at the Meeting
Held on May 22-23 1997, Recommendation 3.''
Mulry, Mary, and Bruce D. Spencer. ``Accuracy of the 1990 Census and
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Association 88 (September 1993): 1080-91.
Norwood, Janet L., Chair, National Academy of Sciences Panel to
Review the 2000 Census. Letter to Kenneth Prewitt, U.S. Department
of Commerce, Bureau of the Census, 3 May 1999.
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Robinson, J.G., B. Ahmed, P. Das Gupta, and K. A. Woodrow.
``Estimates of Population Coverage in the 1990 United States Census
Based on Demographic Analysis.''
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1061-77.
Steffey, Duane L., and Norman M. Bradburn. Counting People in the
Information Age. Washington, D.C.: National Academy Press, 1994.
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and Operations Memorandum Series Chapter S-DT-01.
____. ``Accuracy and Coverage Evaluation: Overview of Design.'' By
Danny R. Childers and Deborah A. Fenstermaker, 11 January 2000.
____. ``Accuracy and Coverage Evaluation Survey: Dual System
Estimation.'' By Donna Kostanich and Richard Griffin, 12 January
2000.
____. ``Accuracy and Coverage Evaluation Survey: Final Post-
stratification Plan for Dual System Estimation.'' By Richard Griffin
and Dawn Haines. DSSD Census 2000 Procedures and Operations
Memorandum Series Chapter Q-24, 19 April 2000.
____. ``Accuracy and Coverage Evaluation Survey: Targeted Extended
Search Plans.'' By Alfredo Navarro. DSSD Census 2000 Procedures and
Operations Memorandum Series Chapter Q-18, 12 January 2000.
____. ``Additional Research on Accuracy of Adjusted Versus
Unadjusted 1990 Census Base for Use in Intercensal Estimates.''
Addendum to Report of the Committee on Adjustment of Post Censal
Estimates, 25 November 1992.
____. ``Analysis of CAPE Findings on 1990 PES Technical Issues.'' By
Sally M. Obenski, 9 June 2000.
____. ``Analysis of CAPE Findings on PES Accuracy at Various
Geographic Levels.'' By Sally M. Obenski and Robert E. Fay, 9 June
2000.
____. ``An Analysis of the Consistency of the 1990 Mosbacher
Guidelines to U.S. Census Bureau Standards.'' By Sally M. Obenski
and Robert E. Fay, 16 May 2000.
____. ``Assessment of Accuracy of Adjusted Versus Unadjusted 1990
Census Base for Use in Intercensal Estimates,'' Report of the
Committee on Adjustment of Postcensal Estimates, 7 August 1992.
____. ``Characteristics of Census Errors.'' By Deborah Griffin and
Christopher Moriarity. 1990 Decennial Census Preliminary Research
and Evaluation Memorandum No. 179, 15 September 1992.
____. ``Master Activity Schedule for Census 2000.''
____. ``Minutes of the Executive Steering Committee on Accuracy and
Coverage Evaluation (A.C.E.) Policy (ESCAP),'' 5 January 2000.
____. ``Non-Response in Census Coverage Measurement Surveys and Its
Impact ``An Historical Review.'' By Ruth Ann Killion. DSSD Briefs,
Information, and Topics Memorandum Series No. 44C, 17 September
1998.
____. ``Reinventing the Decennial Census.'' Global Report of the
Task Force for Planning the Year 2000 Census, June 1995.
____. ``Report of the Working Group on the Use of Demographic
Analysis in Census 2000.'' By William R. Bell, Campbell J. Gibson,
Prithwis Das Gupta, Gregory K. Spencer, J. Gregory Robinson, Mary H.
Mulry, Elizabeth A. Vacca, Robert E. Fay, and Charlene A. Leggieri,
6 May 1996.
____. ``Report to Congress--The Plan for Census 2000.'' Originally
issued July 1997, revised and reissued August 1997.
____. ``Some Results from the Census 2000 Dress Rehearsal.'' By
Rajendra Singh. DSSD Census 2000 Dress Rehearsal Memorandum Series
A-76, 26 February 1999
____. ``Technical Assessment of the Accuracy of Unadjusted Versus
Adjusted 1990 Census Counts.'' Report of the Undercount Steering
Committee, 21 June 1991.
____. ``Updated Summary: Census 2000 Operational Plan,'' February
1999.
U.S. Bureau of Labor Statistics. Abraham, Katharine, Letter to Harry
A. Scarr, U.S. Department of Commerce, Bureau of the Census, 1
December 1993.
U.S. Congress. House. Decennial Census Improvement Act of 1991,
102nd Cong., 2nd sess., H.R. 3280. Congressional Record. Daily ed.
(9 October 1991), H7694.
____. Committee on Government Reform and Oversight. Prepared
Testimony of K.W. Wachter and D.A. Freeman Before the House
Committee on Government Reform and Oversight, 104th Cong., 1st
sess., 29 February 1996.
U.S. Department of Commerce. ``Adjustment of the 1990 Census for
Overcounts and Undercounts of Population and Housing: Notice of
Final Decision.'' Federal Register (22 July 1991) vol. 56 pp. 33582-
642.
____. ``Census 2000 Dress Rehearsal Shows Undercount Persist;
Scientific Methods Correct Race and Ethnic Differential.'' Commerce
News, 20 April 1999, CB 99-CN. 16 (revised).
____. ``Decision of the Director of the Bureau of the Census on
Whether to Use Information from the 1990 Post Enumeration Survey
(PES) to Adjust the Base for the Intercensal Population Estimates
Produced by the Bureau of the Census.'' Federal Register (4 January
1993) vol. 58, no. 1, pp. 69-78.
____. ``Final Guidelines for Considering Whether or not Statistical
Adjustments of the 1990 Decennial Census of Population and Housing
Should be Made for Coverage Deficiencies of the Population.''
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____. ``Position on Adjustment of the 1980 Census Counts for
Underenumeration.'' Federal Register (16 December 1980) vol. 45, no.
243, pp. 82872-85.
U.S. General Accounting Office. Decennial Census: 1990 Results Show
Need for Fundamental Reform. Report to Congressional Requesters, 9
June 1992, 49 GAO/GGD-92-94.
U.S. President, Executive Office. Office of Management and Budget.
``Revisions to the Standards for the Classification of Federal Data
on Race and Ethnicity.'' Federal Register (30 October 1997) vol. 62,
no. 210, pp. 58782-90.
Wachter, Kenneth, and David Freedman. ``Local Heterogeneity and
Census Adjustment for the Intercensal Base.'' Technical Report No.
381. Berkeley, CA: University of California, Department of
Statistics, 1993.
White, Andrew A., and Keith F. Rust, eds. Sampling in the 2000
Census: Interim Report I. Washington, D.C.: National Academy Press,
1996.
____. Preparing for the 2000 Census: Interim Report II. Washington,
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Wright, Tommy and Joyce Farmer. ``A Bibliography of Selected
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ed., 1 May 2000.
June 13, 2000.
MEMORANDUM FOR KENNETH PREWITT
From: William M. Daley
Attached is my decision adopting the analysis and conclusions
set forth in ``Accuracy and Coverage Evaluation: Statement on the
Feasibility of Using Statistical Methods to Improve the Accuracy of
Census 2000.''
The Department of Commerce and the Census Bureau are committed
to making certain that the decennial census, the largest peacetime
mobilization in our country's history, produces the most accurate
count possible of the individuals in our Nation. The census is an
important civic undertaking designed to find out who we are and how
we live. We owe it to the American people to use all of the tools at
our disposal to make the census as accurate as possible.
For decades, the experts at the Census Bureau and within the
statistical community have recognized that the methodology used in
the past fails to count many Americans. This phenomenon `` called
the undercount `` has been measured since the 1940s. More
disturbing, however, is the established fact that the undercount
operates differently for different population groups, creating an
inequity called the differential undercount. Despite the Census
Bureau's best efforts, the differential undercount has persisted
and, for at least the last 50 years, has meant that some groups in
the population are undercounted and therefore underrepresented in
political, resource-allocation, and other decisions.
The choice we face is whether to use modern statistical methods
to produce a more accurate census, or whether we do nothing. Under
the law, statistical methods may not be used in tabulating the
population for purposes of apportioning seats in the House of
Representatives, but I am required to authorize the use of modern
statistical methods, if ``feasible,'' for all other releases of
census data.
[[Page 38396]]
The Director of the Census, with guidance from the Department
concerning the relevant legal standard, has provided an analysis of
the feasibility of using statistical sampling to correct the
persistent errors in the census and to improve its accuracy--
``Accuracy and Coverage Evaluation: Statement on the Feasibility of
Using Statistical Methods to Improve the Accuracy of Census 2000.''
As explained in that document, absent the use of statistical methods
there is no way to correct the persistent differential undercount in
Census 2000. With established statistical methods, however, the
Census Bureau believes that it will be able to correct these errors
and improve the overall accuracy of the census by increasing
coverage and reducing the differential undercount.
I hereby adopt the analysis and conclusions of the Director of
the Census set forth in ``Accuracy and Coverage Evaluation:
Statement on the Feasibility of Using Statistical Methods to Improve
the Accuracy of Census 2000.'' As explained in that document, the
expert staff at the Bureau believe that the Accuracy and Coverage
Evaluation Survey, which was designed to measure and correct for the
overall undercount and the differential undercount, should make the
census counts more accurate. As is appropriate, however, no final
decision about whether to correct the census counts can be made
until the operations have been completed and considered by the
Bureau. The Director will make a final decision before April 1,
2001, the deadline by which the Bureau must provide data to the
States for redistricting.
I am also proposing today a regulation that will insulate the
final decision on whether to correct the census counts from even the
appearance of political tampering and will make the decision-making
process as transparent as possible. Because the final decision on
whether to correct the census is a technical decision, the proposed
regulation would delegate my authority over that decision to the
Director of the Census. His decision would, in turn, be informed by
a public recommendation made by a group of career experts at the
Census Bureau. Through this process, we will be able to ensure
public confidence in the final decision.
Dated: June 13, 2000.
William M. Daley,
Secretary of Commerce.
June 12, 2000.
MEMORANDUM TO: The Secretary, The Director of the Census
FROM: Andrew J. Pincus
SUBJECT: Legal Obligation to Produce Statistically-Corrected Non-
Apportionment Census Numbers
As you know, the Department of Commerce and the Census Bureau
have been reviewing what process to use in determining whether to
statistically correct census data for purposes other than
apportionment of the House of Representatives. As part of this
review, we have examined the legal requirements of the Census Act.
After careful analysis, we have concluded that Section 195 of the
Census Act requires the Census Bureau, if feasible, to produce
statistically-corrected numbers from the decennial census for all
non-apportionment purposes.
The feasibility determination is a technical decision that
should be made by the Director, to whom the Secretary delegated his
Title 13 responsibilities in Departmental Organizational Order 35-2A
(July 22, 1987). To this end, we also believe it appropriate to
propose a regulation that would make certain that the Director has
final authority over the feasibility determination.
I. Background
The Constitution requires Congress to apportion seats in the
House of Representatives among the States every ten years based on
the results of the decennial census, providing that ``[t]he actual
Enumeration shall be made within three Years after the first Meeting
of the Congress of the United States, and within every subsequent
Term of ten Years, in such Manner as they [Congress] shall by Law
direct.'' \1\ Through the Census Act, which is codified in title 13
of the United States Code, Congress has delegated its broad
authority over the census to the Secretary of Commerce.\2\ In
particular, 13 U.S.C. 141(a) provides that the Secretary of Commerce
shall take ``a decennial census of [the] population * * * in such
form and content as he may determine, including the use of sampling
procedures and special surveys.'' As the Supreme Court recognized in
Wisconsin v. City of New York, the Secretary's determination as to
how to conduct the Census, pursuant to the delegation of authority
provided to him by Congress, need only be reasonable, so long as it
is also ``consistent with the constitutional language and the
constitutional goal of equal representation.'' Id. at 19. The Court
further recognized, in the context of the Secretary's decision in
1990 not to adjust the census, that the ``Constitution itself
provides no real instruction'' on what methods the Secretary should
use in performing the Census. Id. at 18.
---------------------------------------------------------------------------
\1\ Constitution, Art. I, Sec. 2, Cl. 3.
\2\ Wisconsin v. City of New York, 517 U.S. 1 (1996).
---------------------------------------------------------------------------
II. Section 195 of the Census Act Requires the Census Bureau To Use
Sampling When ``Feasible'' For Calculating the Population For Purposes
Other Than Apportionment of Seats in the House of Representatives Among
the States
Section 195 of the Census Act states:
Except for the determination of population for purposes of
apportionment of Representatives in Congress among the several
States, the Secretary shall, if he considers it feasible, authorize
the use of the statistical method known as ``sampling'' in carrying
out the provisions of this title.
13 U.S.C. 195. Section 195 refers specifically to only one of the many
uses of census data. Decennial census data are used not only by the
U.S. Congress for apportioning seats in the House of Representatives
among the States, but also by the States in drawing the lines for
congressional and state and local legislative districts, and by federal
and state agencies in allocating funds.
In Department of Commerce v. House of Representatives, 119 S. Ct.
765 (1999), the Supreme Court held that Section 195 does not permit the
use of sampling to produce population counts for the purpose of
apportioning seats in the House of Representatives among the States.
Id. at 777 (``there is only one plausible reading of the amended
Sec. 195: It prohibits the use of sampling in calculating the
population for purposes of apportionment.''). Here, the question is
what standard Section 195 applies with respect to the calculation of
population by the Census Bureau for purposes other than ``apportionment
of Representatives in Congress among the several States.'' The plain
language of the provision supplies the answer: Section 195 states that
the Secretary ``shall'' authorize the use of statistical sampling for
all other purposes ``if he considers it feasible.'' Thus, when
calculating population or other information for a purpose other than
apportionment, the Secretary (or his designee, the Census Bureau) must
first determine whether it is ``feasible'' to use sampling, and--if the
use of sampling is feasible--its use must be authorized.
This interpretation of Section 195's plain language is confirmed by
Congress's amendment of the provision in 1976. Prior to that amendment,
Section 195 stated:
Except for the determination of population for apportionment
purposes, the Secretary may, where he deems it appropriate,
authorize the use of the statistical method known as `sampling' in
carrying out the provisions of this title.
The pre-1976 wording (``may, where he deems it appropriate'') gave the
Secretary the option of using sampling. The 1976 amendment eliminated
the Secretary's discretion, transforming Section 195 into a mandatory
directive --the Secretary ``shall * * * authorize the use of'' sampling
for all other purposes ``if he considers it feasible.'' The Census Act
therefore unambiguously requires, with respect to non-apportionment
calculations, that when sampling is feasible, it must be used.
The Supreme Court's recent decision in Department of Commerce v.
House of Representatives confirms this conclusion. In explaining the
purpose of the 1976 amendments, the Court stated, ``[t]hey changed a
provision that permitted the use of sampling for purposes other than
apportionment into one that required that sampling be used for such
purposes if `feasible.' 119 S.Ct. at 778. The Court explained that
[[Page 38397]]
``section [195] now requires the Secretary to use statistical sampling
in assembling the myriad demographic data that are collected in
connection with the decennial census. But the section maintains its
prohibition on the use of statistical sampling in calculating
population for purposes of apportionment.'' 119 S.Ct. at 777.
III. The Census Bureau's Calculation of Population for the Purpose of
Redistricting is Subject to Section 195's ``Feasib[ility]'' Standard
Section 141(c) of the Census Act permits the ``officers or public
bodies having initial responsibility for the legislative apportionment
or districting of each State'' to submit to the Secretary ``a plan
identifying the geographic areas for which specific tabulations of
population are desired.'' The same provision directs the Secretary to
report such ``[t]abulations of population,'' as well as the ``basic
tabulations of population'' for States that have not submitted a plan,
within one year of the decennial census date. It is clear that these
population tabulations are not ``the determination of population for
purposes of apportionment of Representatives in Congress among the
several States'' (Section 195), and therefore are subject to Section
195's directive that the use of sampling ``shall'' be authorized if
``feasible.''
To begin with, the population tabulations supplied to the States
pursuant to Section 141(c) simply are not made or used for purposes of
apportioning seats in the House of Representatives among the States.
Section 141(c) makes clear that it relates to tabulations for
``legislative apportionment or districting of each State.'' And a
separate subsection of Section 141--subsection (b)--governs the
``tabulation of total population by States * * * as required for the
apportionment of Representatives in Congress among the several
States.'' Indeed, the distinction between these two groups of
calculations is confirmed by their different due dates: the latter set
of numbers must be completed three months earlier than the
redistricting information required by Section 141(c). See also Section
141(e)(2) (distinguishing between use of census data for
``apportionment of Representatives in Congress among the several
States'' and for ``prescribing congressional districts'').
Some commentators have suggested that the term ``apportionment''
within Section 195's ``[e]xcept'' clause encompasses population
calculation for the purposes of redistricting as well as for the
purpose of allocating seats in the House of Representatives among the
States. That position is inconsistent with the plain language of the
statute. First, it ignores the clear distinction in Section 141 between
these two categories of calculations. Second, Congress in 1976 revised
the ``[e]xcept'' clause, replacing the word ``apportionment'' with the
phrase ``apportionment of Representatives in Congress among the Several
States.'' It is difficult to imagine how Congress could have more
clearly evidenced its intent to limit Section 195's prohibition against
the use of sampling to the calculation of population used to allocate
among the States seats in the House of Representatives. And because
Section 141(c) specifically refers to tabulations for redistricting
purposes, but that reference does not appear in the ``[e]xcept'' clause
of Section 195, it is plain that redistricting tabulations are not
encompassed within the Section 195 prohibition. \3\
---------------------------------------------------------------------------
\3\ Some commentators have argued that the Supreme Court reached
a different conclusion in Department of Commerce because it found
standing ``on the basis of the expected effects of the use of
sampling in the 2000 census on intrastate redistricting'' (119 S.
Ct. at 774). The Court's standing decision, however, simply reflects
a conclusion that an individual claiming injury by the use of that
data for redistricting had alleged sufficient Article III injury in
fact to challenge the plan. But the Census plan before the Court
provided for the collection and production of a single set of
sampling-adjusted data for use in both the apportionment tabulation
and the redistricting tabulation. Because the Court invalidated the
plan, there was no need for the Court to apply Section 195 to the
use of sampling for redistricting purposes in order to redress these
plaintiffs' purported injury. This conclusion is confirmed by the
Court's careful limitation of its holding: ``The District Court
below * * * concluded that the proposed use of statistical sampling
to determine population for purposes of apportioning congressional
seats among the States violates the Act. We agree.'' 119 S. Ct. at
765.
robop...@us.govnews.org
Posting-number: Volume 65, Issue 119, Page 38373, Part 1
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Finally, some commentators have suggested that as a practical
matter these two sets of numbers are inextricably linked, asserting--
for example--that it would be a plainly improper result if the Section
141(c) population tabulation of a State for redistricting purposes did
not equal the Section 141(b) apportionment population tabulation for
that State. Nothing in the Census Act requires that result and,
moreover, the two totals have not been equal in the past. For example,
government personnel stationed overseas are included in a State's
Section 141(b) tabulation, but are not included in the data provided to
that State under Section 141(c). Congress could have required such
equality in either Section 141 or Section 195, but it did not do so.
Rather, Congress in Section 141 expressly distinguished between the two
categories of calculations.
The Census Act thus clearly directs that statistical sampling
``shall'' be used in tabulating population for the purposes set forth
in Section 141(c) if the Secretary considers it ``feasible'' to do so.
Even if the plain language of the Act were not clear on this point, we
believe that this interpretation is most consistent with the purposes
of the Census Act and that adopting such an interpretation is within
your discretion. In Wisconsin v. City of New York, 517 U.S. 1 (1996),
the Supreme Court unanimously concluded ``the wide discretion bestowed
by the Constitution upon Congress, and by Congress upon the
Secretary,'' mandates substantial judicial deference to the Secretary's
determinations with respect to the decennial census (517 U.S. at 19).
Given the long history of the use of sampling by the Census Bureau, and
the importance of obtaining the most accurate population tabulations
possible--because of the constitutional significance of the ``one
person, one vote'' principle and of the equal protection principles
reflected in the Voting Rights Act--interpreting the statute to permit
the use of sampling when feasible is the most appropriate approach. The
alternative interpretation would bar the use of statistical sampling
even if the use of sampling would lead to more accurate results, a
construction that conflicts with the basic goal of the decennial
census--to obtain an accurate count of the persons within the United
States.
IV. The Standard For the Feasibility Determination
Section 195 does not contain a definition of the term ``feasible.''
The dictionary definition of the term ranges from the most common
``capable of being done or carried out'' to ``capable of being used or
dealt with successfully, suitable'' or ``reasonable, likely.''
Webster's Ninth New Collegiate Dictionary (1990). The Supreme Court has
considered the word ``feasible'' in other contexts and found that the
plain meaning of the term generally denotes the first and broadest
definition--``capable of being done.'' In American Textile Mfrs.
Institute, Inc. v. Donovan, 452 U.S. 490, 509 (1981), the Court
interpreted the term ``to the extent feasible'' to preclude the
Secretary of Labor from engaging in a cost-benefit analysis of a public
health standard; as the Court explained, Congress itself, by requiring
a standard ``to the extent feasible'' had made the policy choice for
the Secretary. See also Citizens to Preserve Overton Park, Inc. v.
Volpe, 401 U.S. 402, 411 (1971) (``the requirement that there be no
'feasible
[[Page 38398]]
alternative' route admits of little administrative discretion.'').
We understand the term ``feasible'' in accordance with its ordinary
meaning and the overall purposes of the Census Act. It also must be
understood in terms of the uses to which non-apportionment census data
are put, including, among other things, redistricting and allocation of
federal funds. While in other contexts it might be appropriate to
understand ``feasible'' to mean ``possible,'' given the obvious
importance of obtaining the most accurate population (and other)
tabulations possible, it would seem most appropriate to construe that
term in a manner that focuses upon promoting accurate census results.
\4\ Thus, with respect to the proposed use of statistical sampling for
data to be released to the States under Section 141(c), such use is
``feasible'' within the meaning of Section 195 if (1) the proposed use
of sampling is compatible with the other aspects of the census plan,
and with any statutory, timing, and funding constraints; and (2) the
proposed use of statistical sampling would improve the overall accuracy
of the census data.
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\4\ Of course, in other contexts where there is no independent
requirement that the population court be conducted without the use
of sampling (unlike the decennial census, where the statue as
construed by the Supreme Court prohibits the use of sampling for
apportionment of seat in the House of Representatives), the analysis
might also take greater account of the efficiencies that could be
gained by substituting sampling for those other methods.
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The two components of ``feasibility `` can be termed ``operational
feasibility'' and ``technical feasibility.'' These are matters that are
properly within the expert judgment of the Census Bureau. The Census
Bureau's extensive experience in the conduct of the census, the use of
statistical sampling techniques, and the measurement of accuracy should
be the basis for these essentially technical judgments.
V. The Decisionmaking Process
The determination whether the use of sampling is ``feasible'' under
Section 195 should be based upon the information before the
decisionmaker at the time the determination is made. Public Law No. 94-
171 requires the Census Bureau to deliver official census data to the
states for redistricting purposes by April 1, 2001. 13 U.S.C. 141(c).
As with every decennial census, the Census Bureau will conduct
extensive analyses on the census data in the ensuing years. In order to
make a final decision on whether to deliver statistically corrected
data for redistricting purposes, the Census Bureau need only consider
the evidence available to it at the time of its decision to determine
whether the statistically corrected numbers are more accurate and
therefore that the use of sampling is ``feasible'' as that term is
defined herein. See, e.g., Vermont Yankee Nuclear Power Corp. v Natural
Resources Defense Council, 435 U.S. 519, 552-54 (1978) (review of
agency decision must be made based on information available at the time
the decision was made); ICC v. New Jersey, 322 U.S. 503, 514 (1970).
The Census Bureau is in the process of completing a document which
will provide information concerning its assessment of whether using
statistically sampling is feasible with respect to the release of P.L.
94-171 data. Although, as the document will indicate, the Census Bureau
has determined that the use of statistical sampling is operationally
feasible and should improve the accuracy of the census, no final
decision will be made with respect to the release of data until after
the Bureau has had the opportunity to review whether census operations
were conducted in a way that met expectations. This document will be
published in the Federal Register, along with a proposed regulation
that would delegate to the Director of the Census the Secretary of
Commerce's authority to make the final, technical decision on what
numbers to release and would set forth a process for the Census
Bureau's consideration of what numbers to release.
Robert J. Shapiro,
Under Secretary for Economic Affairs.
[FR Doc. 00-15348 Filed 6-14-00; 8:45 am]
BILLING CODE 3510-07-P