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st: RE: subpopulation in the svy command


From   "Sayer, Bryan" <BSayer@s-3.com>
To   "'Guanghui Li '" <guanghui@u.washington.edu>, "'statalist@hsphsun2.harvard.edu '" <statalist@hsphsun2.harvard.edu>
Subject   st: RE: subpopulation in the svy command
Date   Mon, 31 Mar 2003 09:11:43 -0500

The coefficients should be the same provided everything is IDENTICAL between
the two runs.  My guess is that there is missing data involved somewhere.

Bryan Sayer
Statistician, SSS Inc. 

-----Original Message-----
From: Guanghui Li
To: statalist@hsphsun2.harvard.edu
Cc: Jodie
Sent: 3/31/03 1:26 AM
Subject: st: subpopulation in the svy command

Dear all,
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?

Thank you in advance for your help.
Guanghui Li



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