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Re: st: svy subpop option and e(sample)

From   Steven Samuels <>
Subject   Re: st: svy subpop option and e(sample)
Date   Thu, 26 May 2011 22:54:19 -0400


I should also have asked the nature of the subpopulation--whether it was defined by characteristics of the PSUs (e.g. region), so that a PSU was either in or out, or by characteristics of observations within PSUs, so that a PSU could contain  people in and people out of the subpopulation. If the former, is the subpopulation one of the original sampling strata?



The relevant number would be the number of PSUs. If that is 300,000, I would think that it's much more than enough. If you don't mind my asking, what kind of sample had 75 million observations? I usually encounter numbers like that only in census data.  



You said in an earlier message: For a large enough subpopulation, the
correct standard error for the ratio is indistinguishable from the
standard error that assumes that the sample size was fixed (Lohr,
2009, p. 135, shows the formula for a SRS).

How large is large enough? I am facing a similar problem. I extracted
my subpopulation of interest and have 300,000 observations. My
original data had 75 million observations with 61 variables. I cannot
use the entire data due to insufficient RAM on my computer (I will
need about 30-odd GB of RAM to analyze the data as a whole). I had to
ask someone with access to such a powerful machine to extract the data
for me.

If the standard errors for data this large are not going to be very
biased, I can report the variance estimation issue as a limitation of
the analysis. If the data are not large enough, then I will need to
compute dummy variables for all PSUs not represented in the extracted

I would appreciate any help on the matter.

Hitesh S. Chandwani
University of Texas at Austin
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