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Re: st: St: collapse by _N


From   "Michael N. Mitchell" <Michael.Norman.Mitchell@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: St: collapse by _N
Date   Wed, 20 Oct 2010 00:14:43 -0700

Dear Ric

In addition to the great answers Chris and Ulrich sent, I might suggest that you include a variable that counts the number of valid observations. After having the collapsed file, you could then decide what you might want to use as a threshold for the data being too unreliable. You can see more examples about collapsing, including examples using count, at http://www.ats.ucla.edu/stat/stata/modules/collapse.htm .

I hope this helps,

Michael N. Mitchell
Data Management Using Stata      - http://www.stata.com/bookstore/dmus.html
A Visual Guide to Stata Graphics - http://www.stata.com/bookstore/vgsg.html
Stata tidbit of the week         - http://www.MichaelNormanMitchell.com



On 2010-10-19 11.35 PM, Eric Uslaner wrote:
Greetings,

I have a survey data set with respondents geocoded.  I want to collapse the data set to the geocode level, so the simple command would be:

collapse varlist,by(geocode)

However some geocodes barely have any respondents and any collapsed data would be unreliable.  Is there a straightforward way to collapse only if the number of respondents is>  20 (e.g.)?

Many thanks,

Ric




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