st: re: balanced sub-panel to test for selection bias

[Kit Baum <baum@bc.edu>]

sacrificial samovar

Olga wrote

Thank you very much for your help, but last command
results in removing
ALL my observations. Maybe I am doing smth wrong?


egen nfarm = count(farm),by(year)
summarize nfarm, meanonly
by year: keep if nfarm == `r(max)'


Yes, you must be doing something wrong (perhaps mangling the  
punctuation around r(max)?) as it must be true that at least one farm  
has the maximum number of observations signalled by the summarize  
command. Try putting in

tab nfarm

after the summarize and see what the distribution of the count is in  
your sample. I tried this with a hacked version of the Grunfeld data  
and it worked fine.  Then take out the -tab- and try the lines above  
exactly as punctuated.



Kit Baum, Boston College Economics and DIW Berlin
http://ideas.repec.org/e/pba1.html
An Introduction to Modern Econometrics Using Stata:
http://www.stata-press.com/books/imeus.html


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