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st: Re: Different results from svy: tab vs. svy: prop


From   "Michael Blasnik" <michael.blasnik@verizon.net>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: Re: Different results from svy: tab vs. svy: prop
Date   Tue, 24 Oct 2006 10:49:27 -0400

...
I'm not 100% sure about this, but I think the problem may be that the stdweights are being rescaled. For the svy prop commands, the -if year==- condition makes them scaled in the way you would expect, but with the svy tab command, the entire population of both years is included in the calculation and the rescaling changes the results.

If you changed the svy prop commands to use the over(year) option, then the output may match the svy tab output (which may not be what you want). If you also added the nostdrescale option then it may revert back to the estimates you have. I think I would try to stick with commands that use the -if year==xxx- approach as much as possible when dealing with combining more than one survey (vs. the usual caveat of using subpop rather than if).

Michael Blasnik


----- Original Message ----- From: <Arnold.Levinson@UCHSC.edu>
To: <statalist@hsphsun2.harvard.edu>
Sent: Tuesday, October 24, 2006 10:04 AM
Subject: st: Different results from svy: tab vs. svy: prop



Friends,

I'm comparing tobacco survey data for two years. I want to standardize
estimates for the later year (2005) using age-sex-ethnicity distribution
of the earlier year (2001). When I run the estimates separately using -
svy: prop - I get the expected results: std-ized and non-std-ized
estimates are essentially the same for 2001 but different for 2005.
However, when I run the contrast directly using - svy: tab - the
std-ized estimates change by 0.1% for 2001 (the reference year for
std-ized weights) but don't change for 2005. Can someone explain why
this happens? Here's the output.
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