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Re: st: svyset problem 2: using svy with partially complete surveys


From   "Michael I. Lichter" <mlichter@buffalo.edu>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: svyset problem 2: using svy with partially complete surveys
Date   Thu, 24 Sep 2009 17:46:05 -0400

Peter,

Your question is whether we can or should, in theory, correct variance estimates for the size of the sample relative to the population within each poststratum, just as is done for "real" strata. It's not a question that ever occurred to me before, but it does make sense. I don't see why this could not be done, although it may be mooted by the poststratification adjustments to variance calculation that Stata does. Perhaps somebody more knowledgeable than me can answer you properly.

Also, you said:
An alternative I've considered is to define strata that identify
unique combinations of lep and gender and then feeding this
information to the poststratification options in svyset.  Problem here
is that each PSU, school, now overlaps two strata--one for each gender
in that school--and it's not clear what the FPC numbers should be for
each strata.  Am guessing this arrangement will probably violate
assumptions behind svy.
If you were going to create a poststratum-specific FPC, it would be at the student level, not the school level. The original FPC is at the school level because that's how you sampled. In creating poststrata defined by student characteristics, you are in effect pretending that you sampled students, not schools. Your stratum-specific FPC would be at the student level, so cross-classification of schools is not a problem.

As for your missing data problem, either using complete cases only or following Nick's suggestion about imputation are both probably better solutions to your problem than performing some analyses on some cases and other analyses on other cases.

Michael
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