Mean/Median/SD calculation help
gopilth
I have 100 subjects with 6 visits over a period of 6 month and their
weight recorded at each visit. how can I calculate mean and SD of each
subject's weight (all 6 visits),for all 100 subjects. Any help is
appreciated.
Also,
I have 100 subjects with 6 visits over a period of 6 months. some may
have less then 6 visits. how can i calculate the total subjects with
more than or equal to 2 visits and also the median.
Eric A. Booth
It's easier to answer these questions if you provide an example/snippet of your data.
I assume your data is in long format, if so, section 1 below creates some fake data that matches your description (unbalanced panels of 100 subjects with somewhere between 1 and 6 visits).
For your 2 questions, the trick is using the -bysort- prefix along with -egen- to calculate a "panel" mean, sd, etc.
See -help egen- and -help bysort- for more information:
*******************! Paste the code below into the do-file editor and click "do"
clear
//1. create some fake date data to work with//
set obs 100
g subject = _n
expand 6 if inrange(subject, 1, 20)
expand 4 if inrange(subject, 71, 98)
expand 2 if inrange(subject, 31, 69)
expand 1 if inrange(subject, 21, 30)
sort subject
**at this point you should have 100 subjects
**with somewhere between 1 and 6 visits
bys subject: g date = date("01/01/2008", "MDY")+ _n
format date %td
bys subject: g weight = 125+int((200-125+1)*runiform())
/*
Question 1: "How can I calculate mean and SD of each
subject's weight (all 6 visits),for all 100 subjects."
*/
bys subject: egen mean_weight = mean(weight)
bys subject: egen sd_weight = sd(weight)
/*
Question 2: "Some may have less then 6 visits.
How can i calculate the total subjects with
more than or equal to 2 visits and also the median"
*/
bys subject: g number_of_visits = _n
**count and median from -summary-**
sum number_of_visits, d
di "Median Visits is: " `r(p50)'
count if number_of_visits >= 2
***or using -tabstat-***
tabstat number_of_visits, stat(median min max N)
*******************!
~ Eric
__
Eric A. Booth
Public Policy Research Institute
Texas A&M University
ebo...@ppri.tamu.edu
Office: +979.845.6754
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