On May 10, 1:09 pm, Leroy Eileen Baxter, a/k/a "Baxter the Usenet
SPAM'er" <
bax...@baxcode.com> wrote:
>
>
>"RD Sandman" <rdsandman@comcast,net> wrote in message
> news:XnsA1BC689CF...@216.196.121.131...
>
>>"Baxter" <
bax...@baxcode.com> wrote in
>> news:kmhk1e$ch7$
1...@speranza.aioe.org:
>
>>> Oh! You want cites?! Where's YOUR cite for "people use guns
>>> all the time for legitimate self defense"??
>
>> Couple of points
>
>> 1. He asked you first.
>
>> 2. From your own government:
>
>> Self-defense with firearms
>
>> *38% of the victims defending themselves with a firearm attacked
>> the offender, and the others threatened the offender with the
>> weapon.
>
> Really?! Afraid to post the source? Because those are 20 year-old
> statistics?
>
> Care to post just the percent of crimes stopped by 'people using guns for
> legitimate self defense'?
>
Firearms and Violence: A Critical Review
Committee on Law and Justice (CLAJ)
[Beginning @ Page 102]
The Use of Firearms to Defend Against Criminals
While a large body of research has considered the effects of firearms
on injury, crime, and suicide, far less attention has been devoted to
understanding their defensive and deterrent effects. Firearms are used
to defend against criminals. For example, the presence of a gun may
frighten a criminal away, thereby reducing the likelihood of loss of
property, injury, or death.
In this chapter, we consider what is known about the extent and nature
of defensive gun use (DGU). Over the past decade, researchers have
attempted to measure the prevalence of defensive gun use in the
population. This measurement problem has proved to be quite complex,
with some estimates suggesting just over 100,000 defensive gun uses
per year and others suggesting 2.5 million or more defensive gun uses
per year.
A primary cause of this uncertainty is the disagreement over the
definition of defensive gun use—in particular, whether it should be
defined as a response to victimization or as a means to prevent
victimization from occurring in the first place. There is also
uncertainty regarding the accuracy of survey responses to sensitive
questions and the related problems of how to effectively measure
defensive gun use, the types of questions that should be asked, and
the methods of data collection. These disagreements over definition
and measurement have resulted in prevalence rates that differ by a
factor of 22 or more. While even the smallest of the estimates
indicates that there are hundreds of defensive uses every day, there
is much contention over the magnitude and the details.
Since answers to this debate precede any serious investigation into
other related questions, we focus our attention on summarizing and
rating the DGU estimates from the various gun use surveys. We find
that fundamental problems in defining what is meant by defensive gun
use may be a primary impediment to accurate measurement. Finally,
after reviewing the literature that attempts to count the annual
number of defensive gun uses in the United States, we then consider
the small set of studies that evaluate the effectiveness of firearms
for defense.
COUNTING DEFENSIVE GUN USES
How many times each year do civilians use firearms defensively? The
answers provided to this seemingly simple question have been
confusing. Consider the findings from two of the most widely cited
studies in the field: McDowall et al. (1998), using the data from 1992
and 1994 waves of the National Crime Victimization Survey (NCVS),
found roughly 116,000 defensive gun uses per year, and Kleck and Gertz
(1995), using data from the 1993 National Self-Defense Survey (NSDS),
found around 2.5 million defensive gun uses each year.
Many other surveys provide information on the prevalence of defensive
gun use. Using the original National Crime Survey, McDowall and
Wiersema (1994) estimate 64,615 annual incidents from 1987 to 1990. At
least 19 other surveys have resulted in estimated numbers of defensive
gun uses that are similar (i.e., statistically indistinguishable) to
the results founds by Kleck and Gertz. No other surveys have found
numbers consistent with the NCVS (other gun use surveys are reviewed
in Kleck and Gertz, 1995, and Kleck, 2001a).
To characterize the wide gap in the estimated prevalence rate, it is
sufficient to consider the estimates derived from the NSDS and recent
waves of the NCVS. These two estimates differ by a factor of nearly
22. While strikingly large, the difference in the estimated prevalence
rate should, in fact, come as no surprise. As revealed in Table 5-1,
the two surveys are markedly different, covering different
populations, interviewing respondents by different methods, using
different recall periods, and asking different questions.
The NCVS is an ongoing annual survey conducted by the federal
government (i.e., the Census Bureau on behalf of the Department of
Justice) that relies on a complex rotating panel design to survey a
representative sample of nearly 100,000 noninstitutionalized adults
(age 12 and over), from 50,000 households. To elicit defensive gun use
incidents, the survey first assesses whether the respondent has been
the victim of particular classes of crime—rape, assault, burglary,
personal and household larceny, or car theft—during the past six
months, and then asks several follow-up questions about self-defense.
In particular, victims are asked:
TABLE 5-1 Comparing Sampling Design of the NCVS and NSDS
National Crime Victimization Survey
National Self-Defense Survey
Coverage
•Noninstitutionalized U.S. population, age 12 and over, each year
since 1973
•Defensive gun use questions to victims (self-reported)
•U.S population, age 18 and over, with phones, 1993
•DGU questions to all respondents
Sample design
•Rotating panel design
•Stratified, multistage cluster sample of housing units
•Telephone and personal contacts
•One-shot cross-section
•Stratified by region (South and West oversampled)
•Random digit dialing
Sample size
Approximately 50,000 households and 100,000 individuals
4,997 individuals
Response rate
Approximately 95% of eligible housing units
61% of eligible numbers answered by human beings
Sponsorship
U.S. Census Bureau for U.S. Bureau of Justice Statistics
Research Network
Estimated defensive gun use
116,398 annual incidents using 1993-1994 data from redesigned survey
2,549,862 annual incidents
SOURCE: McDowall et al. (2000: Table 1). Used with kind permission of
Springer Science and Business Media.
Was there anything you did or tried to do about the incident while it
was going on?
Did you do anything (else) with the idea of protecting yourself or
your property while the incident was going on?
Responses to these follow-up probes are coded into a number of
categories, including whether the respondent attacked or threatened
the offender with a gun.
The NSDS was a one-shot cross-sectional phone survey conducted by a
private polling firm, Research Network, of a representative sample of
nearly 5,000 adults (age 18 and over). The survey, which focused on
firearms use, first assessed whether the respondent used a gun
defensively during the past five years, and then asked details about
the incident. In particular, respondents were first asked:
Within the past five years, have you yourself or another member of
your household used a handgun, even if it was not fired, for self-
protection or for the protection of property at home, work, or
elsewhere? Please do not include military service, police work, or
work as a security guard.
If the answer was yes, they were then asked:
Did this incident [any of these incidents] happen in the past 12
months?
The discrepancies in the prevalence estimates of defensive gun use can
and should be better understood. Remarkably little scientific research
has been conducted to evaluate the validity of DGU estimates, yet the
possible explanations are relatively easy to categorize and study. The
two surveys are either (1) measuring something different or (2)
affected by response problems in different ways, or (3) both.
Statistical variability, usually reflected by the standard error or
confidence interval of the parameter, also plays some role but cannot
explain these order of magnitude differences.
Coverage
Perhaps the most obvious explanation for the wide variation in the
range of DGU estimates is that the surveys measure different
variables. In the NSDS, for example, all respondents are asked the gun
use questions. In contrast, the NCVS inquires only about use among
persons who claim to be victims of rape, assault, burglary, personal
and household larceny, and car theft. The NCVS excludes preemptive
uses of firearms, uses that occur in crimes not screened for in the
survey (e.g., commercial robbery, trespassing, and arson), and uses
for crimes not revealed by respondents.1
McDowall et al. (2000) found some evidence that these differences in
coverage play an important role. In an experimental survey that
overrepresents firearms owners, 3,006 respondents were asked both sets
of questions about defensive gun use, with random variation in which
questions came first in the interview. By holding the survey sampling
procedures constant (e.g., consistent confidentiality concerns and
recall periods), the authors focus on the effects of questionnaire
content. Overall, in this experiment, the NCVS survey items yielded
three times fewer reports of defensive gun use than questionnaires
that ask all respondents about defensive uses.
The McDowall et al. (2000) crossover experiment is informative and is
exactly the type of methodological research that will begin to explain
the sharp divergence in gun use estimates and how best to measure
defensive gun use. There remains, however, much work to be done.
1
It is well known, for example, that incidents of rape and domestic
violence are substantially underreported in the NCVS (National
Research Council, 2003).
The sample usedin this survey is not representative, and the methods
shed light on only one of the many competing hypotheses. Furthermore,
this limited evidence is difficult to interpret. Even with a
consistent sampling design, inaccurate reporting may still play an
important role. For example, estimates from an NCVS type of question
would be biased if victims were reluctant to report unsuccessful
defensive gun use. Likewise, the estimates found using the NSDS-type
survey would be biased if respondents report defensive gun uses based
on mistaken perceptions of harmless encounters.
Even if we accept the notion of fully accurate reporting, or at least
consistent inaccuracies across the surveys, details on the cause of
these differences are especially important. If these discrepancies
result because of incomplete reporting of victimization among the
classes considered (e.g., rape and domestic violence) in the NCVS,
then one must address the measurement error questions again.
Certainly, we are interested in the behavior of all victims, not just
those who self-report. If instead, the differences occur because the
NSDS-type question includes preemptive uses, then the relevant debate
might focus on which variable is of interest.
In any case, much of the confusion surrounding the debate seems to
center on what is meant by defensive gun use. Self-defense is an
ambiguous term that involves both objective components about ownership
and use and subjective features about intent (National Research
Council, 1993).2 Whether one is a defender (of oneself or others) or a
perpetrator, for example, may depend on perspective. Some reports of
defensive gun use may involve illegal carrying and possession (Kleck
and Gertz, 1995; Kleck, 2001b), and some uses against supposed
criminals may legally amount to aggravated assault (Duncan, 2000a,
2000b; McDowall et al., 2000; Hemenway et al., 2000; Hemenway and
Azrael, 2000). Likewise, protecting oneself against possible or
perceived harm may be different from protecting oneself while being
victimized.
Given this ambiguity, perhaps one of the more important and difficult
problems is to develop a common language for understanding defensive
and offensive gun use. Uniform concepts and a common language will
serve to facilitate future survey work, guide scholarly discussions,
and enhance understanding of the complex ways in which firearms are
related to crime, violence and injury. More generally, a commonly
understood language can also influence the development of firearms
policy and violence policy more generally.
2
This lack of a clear definition may also contribute to inaccurate
response. If scholars who think about these issues have yet to come up
with a clear definition for the behavior of interest, it may be
unreasonable to rely on the accuracy of respondents whom, in some
cases, may not understand or interpret the question as intended.
http://www.nap.edu/openbook.php?record_id=10881&page=167#p2000ba499960167001
FIGURE 5-1 Stages and outcome of potential criminal encounters.
SOURCE: Adapted from Kleck (1997: Figure 7.1).
Although defining and measuring different types of gun use (both
offensive and defensive) is not a simple matter, a typology similar to
the one developed by Kleck may be a useful starting point (1997:
Figure 7.1). Figure 5-1 provides a rough summary of the development of
a violent or criminal encounter. Firearms and other weapons may be
involved at different points in the development of a crime, from
threats to realized crimes and injury. At each stage of a potentially
threatening encounter, one may be interested in learning about the
basic circumstances, about firearms use and other actions, about the
intent of the respondent, and about outcomes. The relatively
subjective nature of threats, which may or may not develop into
criminal events, may justify placing these uses in a separate category
(Kleck, 2001b:236). More generally, it would seem useful to
distinguish between the more objective and subjective features of
firearms use. Eliciting and interpreting relatively objective
questions about whether and how one uses a gun may be relatively
simple and lead to consensus on these basic matters. Eliciting and
interpreting relatively subjective questions on intent may be much
more complex and less amenable to consensus conclusions.3
Ultimately, researchers may conclude that it is impossible to
effectively measure many aspects of defensive gun use. As noted above,
counting crimes averted before the threat stage, and measuring
deterrence more generally, may be impossible. Successful deterrence,
after all, may yield no overt event to count. Imagine, for example,
measuring defensive gun use for a person who routinely carries a
handgun in a visible holster. How many times has this person “used a
handgun, even it was not fired, for self-protection?” (i.e., the NSDS
definition of defensive gun use). In this regard, much of the debate
on the number of defensive gun uses may stem from an ill-defined
question, rather than measurement error per se.
Response Problems in Firearms Use Surveys
Questions about the quality of self-reports of firearms use are
inevitable. Response problems occur to some degree in nearly all
surveys but are arguably more severe in surveys of firearm-related
activities in which some individuals may be reluctant to admit that
they use a firearm, and others may brag about or exaggerate such
behavior.4 If some sampled individuals give incorrect answers
(inaccurate response) and others fail to answer the survey at all
(nonresponse), investigators may draw incorrect conclusions from the
data provided by a survey.
3
A number of scholars have made explicit recommendations for
collecting detailed narratives on the nature of the event. See, for
example, recommendations made by Cook and Ludwig (1998), Smith (1997),
and Kleck (2000). Hemenway and Azrael (2000) and Hemenway et al.
(2000) collected and analyzed detailed narratives on gun use incidents
that reveal that they are often complex and difficult to categorize.
4
These same measurement problems were discussed in a report by the
National Research Council (2001) that explored the data problems
associated with monitoring illicit drug consumption.
Inaccurate Response
In fact, it is widely thought that inaccurate response biases the
estimates of defensive gun use. Self-report surveys on possibly
deviant behaviors invariably yield some false reports. Responses are
miscoded, and respondents may misunderstand the questions or may not
correctly remember or interpret the event. In addition to these
unintentional errors, respondents may also exaggerate or conceal
certain information.
The literature speculates widely on the nature of reporting errors in
the firearms use surveys.5 Some argue that reporting errors cause the
estimates derived from the NCVS to be biased downward.6 Kleck and
Gertz (1995) and Kleck (2001a), for example, speculate that NCVS
respondents doubting the legality of their behaviors or more generally
fearing government intrusion may be inclined to provide false reports
to government officials conducting nonanonymous interviews.
Furthermore, Smith (1997) notes that NCVS respondents are not directly
asked about firearms use but instead are first asked whether they
defended themselves, and then they are asked to describe in what ways.
Indirect questions may lead to incomplete answers.
Others argue that the estimates from the NSDS and other firearms use
surveys are upwardly biased. Cook and Ludwig (1998), Hemenway (1997a),
and Smith (1997), for example, suggest that the firearms use surveys
do not effectively bound events that occur in prior interviews and
thus may result in “memory telescoping.” That is, respondents in the
NSDS are more likely to report events that occurred prior to the
observation window of interest. Furthermore, McDowall et al. (2000)
speculate that preemptive uses recorded in the NSDS but not generally
covered in the NCVS (which focuses on victims) are susceptible to a
greater degree of subjectivity and thus inaccurate reporting.
A number of other general arguments have been raised as to why these
surveys might be inaccurate. Some suggest that respondents may forget
or conceal events that do not lead to adverse outcomes (Kleck and
Gertz, 1995; Kleck, 2001a), while others suggest that respondents may
exaggerate or conceal events due to social stigma. Some have even
suggested that respondents may strategically answer questions to
somehow influence the ongoing public debate (Cook et al., 1997).
5
See Kleck (2001a) for a detailed review of the various hypotheses
about inaccurate reporting in gun use questionnaires.
6
Kleck argues that the NCVS is well designed and uses state-of-the-art
survey sampling techniques for measuring victimization, but for
exactly those reasons it is not well designed for measuring defensive
gun use.
Finally, Hemenway (1997b) raises what amounts to a mechanical, rather
than behavioral, concernregarding why the DGU estimates may be
generally biased upward. For any rare event, in fact for any event
with less than 50 percent probability, there are more respondents who
can give false positive than false negative reports. Suppose, for
example, in a sample of 1,000 respondents, the true prevalence rate is
1 percent; that is, 10 respondents used a gun defensively. Then 990
may provide false positive reports, while only 10 may provide false
negative reports. Even small fractions of false positive reports may
lead to substantial upward biases. Cook et al. (1997) further suggest
that by focusing on victims, the NCVS reduces the scope of the false
positive problem.
Although the rare events problem may be well known and documented in
epidemiological studies of disease, it is uncertain whether this same
phenomena affects inferences on defensive gun uses as well. People may
have reasons to conceal or exaggerate defensive gun uses that may not
apply when studying rare diseases. In fact, what is known about
accurate reporting of other crime-related activities provides some
evidence to the contrary. Validation studies on the accuracy of self-
reports of illicit drug use among arrestees, for example, suggest that
for this somewhat rare but illegal activity, the numbers of false
reports of use are far less than the numbers of false reports of
abstinence: self-reports of drug use are biased downward (Harrison,
1995).
Although theories abound, it is not possible to identify the
prevalence of defensive gun use without knowledge on inaccurate
reporting. Kleck and Gertz (1995) and others suggest that estimates
from the NCVS are biased downward, arguing that respondents are
reluctant to reveal information to government officials, and that
indirect questions may yield inaccurate reports. Hemenway (1997a) and
others suggest that estimates from the NSDS are biased upward, arguing
that memory telescoping, self-presentation biases, and the rare events
problem more generally lead the numbers of false positive reports to
substantially exceed the numbers of false negative reports. It is not
known, however, whether Kleck’s, Hemenway’s, or some other assumptions
are correct. The committee is not aware of any factual basis for
drawing conclusions one way or the other about reporting errors.
Nonresponse
While inaccurate response has received a great deal of speculative
attention, the problem of nonresponse has hardly been noticed.7
Nonresponse is a problem in survey sampling, but it is especially
problematic in the firearms use phone surveys like the NSDS. Although
not completely revealed by Kleck and Gertz (1995), the response rate
in the NSDS appears to lie somewhere between 14 and 61 percent.8 The
response rate in the NCVS survey is substantially higher, at around 95
percent.
7
Both Duncan (2000b) and Hemenway (1997a) recognize the potential
problems created by nonresponse in the firearms use surveys.
Survey data are uninformative about the behavior of nonrespondents.
Thus, these data do not identify prevalence unless one makes
untestable assumptions about nonrespondents. A simple example
illustrates the problem. Suppose that 1,000 individuals are asked
whether they used a firearm defensively during the past year but that
500 do not respond, so the nonresponse rate is 50 percent. If 5 of the
500 respondents used guns defensively during the past year, then the
prevalence of defensive gun use among respondents is 5/500 = 1
percent. However, true prevalence among the 1,000 surveyed individuals
depends on how many of the nonrespondents used a firearm. If none did,
then true prevalence is 5/1,000 = 0.5 percent. If all did, then true
prevalence is [(5 + 500)/1,000] = 50.5 percent. If between 0 and 500
nonrespondents used a firearm defensively, then true prevalence is
between 0.5 and 50.5 percent. Thus, in this example, nonresponse
causes true prevalence to be uncertain within a range of 50 percent.
Prevalence rates can be identified if one makes sufficiently strong
assumptions about the behavior of nonrespondents. In the DGU
literature, nonresponse is assumed to be random, thus implying that
that prevalence among nonrespondents is the same as prevalence among
respondents. The committee is not aware of any empirical evidence that
supports the view that nonresponse is random or, for that matter,
evidence to the contrary.
External Validity
A number of scholars have suggested that results from the NSDS and
other firearms use surveys are difficult to reconcile with analogous
statistics on crime and injury found in other data.
8
Kleck and Gertz report that 61 percent of contacts with persons for
the NSDS resulted in a completed interview. Presumably, however, there
were also many households in the original sampling scheme that were
not contacted. For example, using data from the National Study of
Private Firearms Ownership (NSPFO), a national phone survey designed
to elicit information about firearms ownership and use, Cook and
Ludwig (1998) report that 29,917 persons were part of the original
sampling scheme, of which 15,948 were determined to be ineligible
(phones not working, not residential, etc.), 3,268 were determined to
be eligible, and the remaining 10,701 were unknown (e.g., no answer,
answering machine, busy, etc.). Of the 3,268 that were known to be
eligible, 2,568 provided complete interviews, for a response rate of
79 percent among contacted households. The 10,701 with unknown
eligibility status must also be accounted for. If none of these
households was actually eligible, than the true response rate would be
79 percent. If, however, all of these are eligible, then the true rate
would be 18 percent [2,568/(10,701 + 3,268)]. Thus, the response rate
in the NSPOF lies between 18 and 79 percent. If the response rates are
consistent across the two surveys, the lower bound response rate for
the NSDS would be 14 percent [ (0.61/0.79)*0.18].
For example, Hemenway (1997a) points out that results from the NSDS
imply that firearms are used defensively in every burglary committed
in occupied households and in nearly 60 percent of rapes and sexual
assaults committed against persons over 18 years of age; that
defensive gun users thought they wounded or killed offenders in
207,000 incidents, yet only 100,000 people are treated in emergency
rooms for nonfatal firearms injuries; and that hundreds of thousands
of persons almost certainly would have been killed if they had not
used a firearm defensively, implying that nearly all potentially fatal
attacks are successfully defended against (Cook and Ludwig, 1998).
Cook and Ludwig (1998), Hemenway (1997a), and others argue that these
and other similar comparisons lead to “completely implausible
conclusions” and go on to suggest that these inconsistencies “only
buttress the presumption of massive overestimation” of defensive gun
uses in the NSDS (Hemenway, 1997a:1444).
Although potentially troubling, the strong conclusion drawn about the
reliability and accuracy of the DGU estimates seems premature. In some
cases, it may be that the comparison statistic is subject to error.
The reported prevalence of rape in the NCVS, for example, is believed
to be biased substantially downward (National Research Council, 2003).
More importantly, however, evidence on the apparent biases of the
estimated incident rates, wounding rates, and counts of averted
injuries does not directly pertain to the accuracy of the DGU
estimates. Kleck and Gertz (1995), in fact, note that victimization
estimates drawn using the NSDS, a survey designed to measure firearms
use rather than victimization, are subject to potential reporting
errors in unknown directions. Cook and Ludwig (1998) find evidence of
reporting errors of crime in the firearms use surveys, with many
respondents reporting that crime was involved on one hand, yet that no
crime was involved on the other. Likewise, questions about whether a
respondent thought he wounded or killed the offender and those
eliciting subjective information on what would have happened had a gun
not been used are also subject to substantial reporting biases. As
noted by Kleck and Gertz (1998), respondents may be inclined to
“remember with favor their marksmanship” and may tend to exaggerate
the seriousness of the event.
In addition to invalid response errors, sampling variability may also
play an important role in these conditional comparisons. Inferences
drawn from the relatively small subsamples of persons who report using
firearms defensively (N = 213 in the NSDS) are subject to high degrees
of sampling error. Using data from the National Study of Private
Firearms Ownership, a survey similar to the NSDS, Cook and Ludwig
(1998), for example, estimate that firearms were used defensively in
322,000 rapes (rape, attempted rape, sexual assault) but report a 95
percent confidence interval of [12,000 to 632,000].9 The lower bound
interval estimate would imply that firearms are used defensively in
less than 3 percent of all rapes and sexual assaults (Kleck, 2001a).
Replication and Recommendations
As indicated above, the estimated numbers of defensive gun uses found
using the NSDS have been reproduced (i.e., are statistically
indistinguishable) in many other surveys. Kleck (2001a:270) suggests
that replication provides ample evidence of the validity of the
findings in the NSDS survey:
The hypothesis that many Americans use guns for self-protection each
year has been repeatedly subjected to empirical test, using the only
feasible method for doing so, survey of representative samples of the
populations. The results of nineteen consecutive surveys unanimously
indicate that each year huge numbers of Americans (700,000 or more)
use guns for self-protection. Further, the more technically sound the
survey, the higher the defensive gun use estimates. The entire body of
evidence cannot be rejected based on the speculation that all surveys
share biases that, on net, cause an over estimation of defensive gun
use frequency because, ignoring fallacious reasoning, there is no
empirical evidence to support this novel theory. At this point, it is
fair to say that no intellectually serious challenge has been mounted
to the case for defensive gun use being very frequent.
Certainly, the numerous surveys reveal some phenomena. In light of the
differences in coverage and potential response errors, however, what
exactly these surveys measure remains uncertain. Ultimately, the
committee found no comfort in numbers: the existing surveys do not
resolve the ongoing questions about response problems and do not
change the fact that different subpopulations are queried. Mere
repetition does not eliminate bias (Rosenbaum, 2001; Hemenway, 1997a).
However, the committee strongly agrees with the main sentiment
expressed by Kleck and others. Evidence from self-reported surveys
will invariably be subject to concerns over reporting errors and other
biases. Still, we can hope to have a greater degree of confidence in
the survey results by relying on replications and survey sampling
experiments that serve to effectively reduce the degree of uncertainty
about the true prevalence rate. The objective of these experiments
should be consistency of results in a variety of sampling designs.
Replications and experiments should disrupt aspects of the original
study to check whether the prevalence estimate is reproduced or
altered under different survey designs. Effective replications will
vary the nature of the potential biases in order to explicitly reduce,
rather than increase, the prospects of reproducing the original
results (Rosenbaum, 2001).
9
Kleck and Gertz (1995) do not report confidence intervals for these
conditional estimates.
These ideas are not new to this controversial literature. McDowall et
al. (2000) do exactly this type of experimental evaluation by holding
certain factors constant—namely, the sampling methodology—but varying
the content of the questionnaire. Other similar experiments or
replications or both could be used to vary the nature of memory
telescoping, social presentation bias, and other plausible factors
that might influence reporting behaviors. In fact, Cook and Ludwig
(1998), Smith (1997), Kleck (2000), and many others make numerous
recommendations for experiments or replications.
The committee strongly believes that these types of studies can and
should be undertaken. Without reliable information, researchers will
continue to be forced to make unsubstantiated assumptions about the
validity of responses and thus about the prevalence of defensive gun
use.
The committee recommends a systematic and rigorous research program to
(1) clearly define and understand what is being measured, (2)
understand inaccurate response in the national use surveys, and (3)
develop methods to reduce reporting errors to the extent possible.
Well-established survey sampling methods can and should be brought to
bear to evaluate the response problems. Understanding response will be
useful for not only explaining the striking gap in DGU estimates but,
more importantly, understanding defensive gun use.
EFFICACY OF SELF-DEFENSE WITH A FIREARM
Accurate measurement on the extent of firearms use is the first step
for beginning a constructive dialogue on how firearms are used in
American society. Invariably, however, attention will turn to the more
important and difficult questions about the consequences of using a
firearm for self-defense. How effective are firearms at preventing
injury and crime? Would gun users have been better off (on average)
using alternative defensive strategies? How does the efficacy of self-
defense vary by circumstance (e.g., abilities of victim and
perpetrator, location of crime, weaponry)?
Answering these questions is essential for evaluating the costs and
benefits of firearms to society. For example, if using a firearm
defensively is no more effective than basic avoidance techniques, then
defensive gun use would have no relative benefit. In contrast, if
firearms are more effective at resisting crime and injury than
alternative methods, then civilian ownership and the use of firearms
may play a vital role in the nation’s ability to deter and fight
crime. Of course, the benefits of defensive gun use must ultimately be
weighed against the potential costs that may arise if firearms are
involved in the final stages of violent criminal encounters: defensive
gun use may lead to relatively higher risks of injury and death to
victims or offenders.
--------------------------------------------------------------------------------
TABLE 5-2 Probability of Injury and Loss Among Victims by Means of
Self-Protection
Method
Robbery
Assault
Injury
Loss
Injury
With gun
12.8
15.2
27.9
All self-protection
34.0
52.8
58.1
No self-protection
23.6
83.6
55.2
All incidents
30.2
69.9
57.4
SOURCE: Adapted from Kleck (2001b:289, Table 7.1).
Finally, both the benefits and costs must be evaluated within the
context of offender weaponry. If criminals were not armed, would
firearms be more or less useful for protecting potential victims? If
the efficacy of self-defense depends on the number of firearms in
society, then partial equilibrium analyses that hold offender weaponry
fixed may not answer the right questions.
Empirical Evidence
While the literature on self-defense has been preoccupied with the
basic measurement questions, a handful of studies assess the efficacy
of defensive gun use.10 Using data from the NCVS, Kleck (2001b)
compares the probability of injury and crime by different defensive
actions. The results, summarized in Table 5-2, suggest that
respondents who use firearms are less likely to be injured and lose
property than those using other modes of protection. For example,
while the overall rate of injury in robbery is 30.2, only 12.8 percent
of those using a firearm for self-protection were injured. Ziegenhagen
and Brosnan (1985) draw similar conclusions about the efficacy of
armed (although not firearm) resistance when summarizing 13 city
victim surveys. Using a multivariate regression analysis, Kleck and
DeLone (1993) confirm these basic cross-tabular findings.11
10
A number of studies use samples of data collected from crimes
reported to police. Police records are presumed to understate
resistance in general and defensive gun use in particular (Kleck,
2001a; Kleck and DeLone, 1993). More importantly, these surveys cannot
reveal successful forms of resistance that are not reported to the
police at all.
11
The committee is not aware of other multivariate analyses of the
effects of resistance with a firearm on crime and injury. Researchers
have, however, evaluated the effects of armed resistance. Using data
from the NCVS, Kleck and Sayles (1990) conclude that rapes are less
likely to be completed if the victim uses armed resistance. Lizotte
(1986) draws similar conclusions using data from city victim surveys.
Defense with a firearm is associated with fewer completed robberies
and less injury. Two forms of self-defense, namely using force without
a weapon and trying to get help or attract attention, are associated
with higher injury rates than taking no self-protective action.
The results suggest interesting associations: victims who use guns
defensively are less likely to be harmed than those using other forms
of self-protection. Whether these findings reflect underlying causal
relationships or spurious correlations remains uncertain. Much of the
existing evidence reports simple bivariate correlations, without
controlling for any confounding factors. Kleck and DeLone (1993) rely
on multivariate linear regression methods that implicitly assume that
firearms use, conditional on observed factors, is statistically
independent of the unobserved factors influencing the outcomes, as
would be the case in a classical randomized experiment.12 Is this
exogenous selection assumption reasonable? Arguably, the decisions to
own, carry, and use a firearm for self-defense are very complex,
involving both individual and environmental factors that are related
to whether a crime is attempted, as well as the outcomes of interest.
13 The ability of a person to defend himself or herself, attitudes
toward violence and crime, emotional well-being, and neighborhood
characteristics may all influence whether a person uses a firearm and
the resulting injury and crime. Thus, in general, it is difficult to
be confident that the control variables account for the numerous
confounding factors that may result in spurious correlations.
Furthermore, the committee is not aware of any research that considers
whether the finding is robust to a variety of methodological
adjustments. Without an established body of research assessing whether
the findings are robust to the choice of covariates, functional form,
and other modeling assumptions, it is difficult to assess the
credibility of the research to date.
The most obvious and fundamental limitation, however, is that the data
on defensive gun uses are, as described above, potentially error
ridden. Without reliable information on the prevalence of defensive
gun use, researchers are forced to make implausible and
unsubstantiated assumptions about the accuracy of self-reported
measures of resistance. For example, Kleck, one of the most vocal
critics of DGU estimates derived from the NCVS, assumes these data are
fully accurate when measuring the efficacy of resistance (Kleck,
2001b; Kleck and DeLone, 1993).
12
Kleck and DeLone (1993) account for basic demographic characteristics
of the victim (e.g., race, gender, age, income, and education) and
some details on the event (e.g, whether the offender had a gun).
13
Not only does the potential of unobserved factors create biases of
unknown magnitude, but it is also difficult to determine the direction
of these biases. If, as suggested by the National Research Council
(1993:266), persons who use firearms were better prepared in general
to defend against crime, then the estimated associations would be
biased upward. In contrast, if firearms are used in more dangerous
situations, then the estimated associations would be biased downward
(Kleck, 2001b:292).
fewer completed robberies and less injury. Two forms of self-defense,
namely using force without a weapon and trying to get help or attract
attention, are associated with higher injury rates than taking no self-
protective action.
The results suggest interesting associations: victims who use guns
defensively are less likely to be harmed than those using other forms
of self-protection. Whether these findings reflect underlying causal
relationships or spurious correlations remains uncertain. Much of the
existing evidence reports simple bivariate correlations, without
controlling for any confounding factors. Kleck and DeLone (1993) rely
on multivariate linear regression methods that implicitly assume that
firearms use, conditional on observed factors, is statistically
independent of the unobserved factors influencing the outcomes, as
would be the case in a classical randomized experiment.12 Is this
exogenous selection assumption reasonable? Arguably, the decisions to
own, carry, and use a firearm for self-defense are very complex,
involving both individual and environmental factors that are related
to whether a crime is attempted, as well as the outcomes of interest.
13 The ability of a person to defend himself or herself, attitudes
toward violence and crime, emotional well-being, and neighborhood
characteristics may all influence whether a person uses a firearm and
the resulting injury and crime. Thus, in general, it is difficult to
be confident that the control variables account for the numerous
confounding factors that may result in spurious correlations.
Furthermore, the committee is not aware of any research that considers
whether the finding is robust to a variety of methodological
adjustments. Without an established body of research assessing whether
the findings are robust to the choice of covariates, functional form,
and other modeling assumptions, it is difficult to assess the
credibility of the research to date.
The most obvious and fundamental limitation, however, is that the data
on defensive gun uses are, as described above, potentially error
ridden. Without reliable information on the prevalence of defensive
gun use, researchers are forced to make implausible and
unsubstantiated assumptions about the accuracy of self-reported
measures of resistance. For example, Kleck, one of the most vocal
critics of DGU estimates derived from the NCVS, assumes these data are
fully accurate when measuring the efficacy of resistance (Kleck,
2001b; Kleck and DeLone, 1993).
12
Kleck and DeLone (1993) account for basic demographic characteristics
of the victim (e.g., race, gender, age, income, and education) and
some details on the event (e.g, whether the offender had a gun).
13
Not only does the potential of unobserved factors create biases of
unknown magnitude, but it is also difficult to determine the direction
of these biases. If, as suggested by the National Research Council
(1993:266), persons who use firearms were better prepared in general
to defend against crime, then the estimated associations would be
biased upward. In contrast, if firearms are used in more dangerous
situations, then the estimated associations would be biased downward
(Kleck, 2001b:292).
http://www.nap.edu/openbook.php?record_id=10881&page=102
Any further questions, Baxter?