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Re: st: Survey variance estimates - large software differences (resend)


From   sjsamuels@gmail.com
To   "Levinson, Arnold" <Arnold.Levinson@ucdenver.edu>
Subject   Re: st: Survey variance estimates - large software differences (resend)
Date   Fri, 10 Jul 2009 16:29:47 -0400

Arnold, it did appear on June 30 and I replied the first time on July
2nd.  Your  post had no subject, so it's not obvious on the list; I
didn't notice that and so I reply did not have an informative subject.
 Here's what I responded..

-Steve


I cannot tell why the SE's are so different. The n's and outcome means
for the subpopulation size total for the "smkskul" are identical in
all three analyses, so that is not a problem.  I do see some issues.

1.  In SAS. the variables in the CLUSTER statement should identify
only the PSUs, the 1st stage units.   This should, however, lead to
smaller, rather than larger standard errors.

2. Stata thinks that there are 46 strata in the entire sample, but SAS
thinks that there are 27.  SUDAAN and SAS differ by about 1,000 in
their report of the sample size for the original population.

3. The subpopulation seems confined to one PSU- one value of "skulid"
- and one stratum,, but Stata says that there arere nine PSUs with
observations in the subpopulation.  Perhaps Stata considers the
second stage units,, class rooms, as PSU's in this case, and the
othefrs do not. If so, this could account for some of the discrepancy:
between-classroom variation could be  be  small, if there are 16
individuals in nine classrooms.

4. The outcome, according to SUDAAN, is missing for 93% of the
subpopulation sample.

I suggest that you make sure that variables and observations are
identical in the data sets (I notice two different weight variables);
make sure that the cluster, classroom, and stratum counts agree in SAS
and Stata.  Rerun your analyses on this outcome and on one with no
missing values and submit your findings to the group with a copy to
Jeff Pitblado at Stata.

Good luck!

Steve
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