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Re: st: subpopulation in the svy command


From   jpitblado@stata.com (Jeff Pitblado, Stata Corp.)
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: subpopulation in the svy command
Date   Tue, 01 Apr 2003 15:25:31 -0600

Guanghui Li <guanghui@u.washington.edu> noticed that -svypoisson- produced
different point estimates when comparing the results of a model fit using -if-
and the -subpop()- option:

> I need to estimate a svypossion model and I am only interested in a
> subpopulation.
> I was curious to see how the "subpop" command would affect my results since
> Stata Manual emphasized the importance of using "subpop" instead of "in".
> Therefore, I estimated two models, one with the "subpop" command, the other
> with the "if" command.
> I was expecting to see different standard errors. However, I got different
> coefficients in addition to different variances.
> Based on what I read from the manual, I got the impression that only
> variances would be affected by using the "if" command.
> Could the coefficients be different?

Bryan Sayer <BSayer@s-3.com> replied that the point estimates should be
the same.

We have looked into this and discovered a small bug.  It has been fixed and
should be available in the next ado update.

--Jeff
jpitblado@stata.com
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