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Re: st: Dealing with survey data when the entire population is also in the dataset


From   "Michael I. Lichter" <MLichter@Buffalo.EDU>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Dealing with survey data when the entire population is also in the dataset
Date   Fri, 24 Jul 2009 23:24:10 -0400

Margo,

1. select your sample and save it in a new dataset, and then in the new dataset:
a. define your stratum variable -stratavar- as you described
b. define your pweight as you described, wt = 1/(sampling fraction) for each stratum 2. combine the full original dataset with the new one, but with stratavar = 1 for the new dataset and wt = 1 and with a new variable sample = 0 for the original and =1 for the sample, and then
a. -svyset [pw=wt], strata(stratavar)-
b. do your chi square test or whatever using svy commands, e.g., -svy: tab var1 sample-

Michael

Margo Schlanger wrote:
Hi --

I have a dataset in which the observation is a "case".  I started with
a complete census of the ~4000 relevant cases; each of them gets a
line in my dataset.  I have data filling a few variables about each of
them.  (When they were filed, where they were filed, the type of
outcome, etc.)

I randomly sampled them using 3 strata (for one strata, the sampling
probability was 1, for another about .5, and for a third, about .75).
I end up with a sample of about 2000.  I know much more about this
sample.

Ok, my question:

1) How do I use the svyset command to describe this dataset?  It would
be easy if I just dropped all the non-sampled observations, but I
don't want to do that, because of question 2:

2) How do I compare something about the sample to the entire
population, just to demonstrate that my sample isn't very different
from that entire population on any of the few variables I actually
have comprehensive data about. I could do this simply, if I didn't
have to worry about weighting:

tabulate year sample, chi2

But I need the weights.  In addition, I can't simply use weighting
commands, because in the population (when sample == 0), everything
should be weighted the same; the weights apply only to my sample (when
sample == 1).  And I can't (so far) use survey commands, because I
don't know the answer to (1), above.

NOTE: Nearly all the variables I care about are categorical:  year of
filing, type of case.  But it's easy enough to turn them into dummies,
if that's useful.


Thanks for any help with this.

Margo Schlanger

______________________
Professor of Law
University of Michigan Law School
Director, Civil Rights Litigation Clearinghouse
(http://clearinghouse.wustl.edu)

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--
Michael I. Lichter, Ph.D. <mlichter@buffalo.edu>
Research Assistant Professor & NRSA Fellow
UB Department of Family Medicine / Primary Care Research Institute
UB Clinical Center, 462 Grider Street, Buffalo, NY 14215
Office: CC 126 / Phone: 716-898-4751 / FAX: 716-898-3536

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