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Re: st: Single stage design and PSU - STATA version 9


From   jpitblado@stata.com (Jeff Pitblado, StataCorp LP)
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Single stage design and PSU - STATA version 9
Date   Fri, 31 Mar 2006 10:10:23 -0600

Pramod Adhikari <pramod.adhikari@abs.gov.au> appears to be getting an
incorrect PSU count (6,333 instead of 402) from -svy:mean- even though
-svydes- reports the correct count:

> I just installed Stata version 9 and I am re-running some analysis that I
> previously used Stata 8.
> The survey data (n=6,333) I am using comes from a multistage design, but I
> only have information on strata (8) and PSU (403) and I treat this data as
> a single stage clustered design. There are a few PSU with one observations
> only.
> 
> However, subsequent 'svy' estimates show the number of PSUs as 6,333
> instead of 403. It did not happen in Stata 8.
> 
> . svyset psu [pw=wt], strata(stateur);
> 
>       pweight: wt
>           VCE: linearized
>      Strata 1: stateur
>          SU 1: psu
>         FPC 1: <zero>
> 
> Then I 'svvydes' to see whether the 'svyset' defined the psu and strata
> correctly .

(output omitted)

> However, when estimating means, the number of PSUs is shown as 6,333.
> 
> . svy: mean violence
> (running mean on estimation sample)
> 
> Survey: Mean estimation
> 
> Number of strata =       8          Number of obs    =    6333
> Number of PSUs   =    6333          Population size  = 6.9e+06
>                                     Design df        =    6325
> 
> --------------------------------------------------------------
>              |             Linearized
>              |       Mean   Std. Err.     [95% Conf. Interval]
> -------------+------------------------------------------------
>     violence |   .0712806   .0039479      .0635415    .0790198
> --------------------------------------------------------------

I do not recall this ever being reported before, and can't reproduce the
problem.  Pramod should make sure Stata 9 is fully up-to-date (including the
-update swap- for the executable).  If that doesn't fix it, Pramod can email
me directly for further assistance.

--Jeff
jpitblado@stata.com
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