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Re: st: collapse if at least X or more obs. per group are non-missing


From   Nick Winter <nw53@cornell.edu>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: collapse if at least X or more obs. per group are non-missing
Date   Wed, 25 Aug 2004 10:52:39 -0400

At 12:19 PM 8/24/2004 -0700, you wrote:
I'd like to convert a panel data set with annual country obs to one of
decadal country averages, excluding those decadal averages for which 5 or
more observations per country are missing within a decade.

My first idea was to use a two step procedure along the lines of:

1. Run:
collapse (mean) GDP (count) GDP , by(country decade)
this should give me a) the decadal averages I want and b) the number of
non-missing obs used to compute each of these decadal averages.

2. replace mean_GDP=. if count_GDP<5 (or whatever STATA will call these vars
saving the means & counting the non-missing obs)
this should set to missing those decadal averages for which 5 or more
observations per country were missing within each decade.
It has already been pointed out that you must give different names to your new variables with this solution.

Another way to go would be:

. bysort country decade: generate N = _N
. collapse GDP if N>5

This would be appropriate, obviously, if you only need the count in order to drop the ones you don't want; if you need it for other things then go ahead with the original twostep procedure.

Nick WINter


--------------------------------------------------------
Nicholas Winter 607.255.8819 t
Assistant Professor 607.255.4530 f
Department of Government nw53@cornell.edu e
308 White Hall falcon.arts.cornell.edu/nw53 w
Cornell University
Ithaca, NY 14853-4601

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