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Re: st: reported subpop no. of observations seems wrong? and is subpop needed with replicate wgts.?


From   jpitblado@stata.com (Jeff Pitblado, StataCorp LP)
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: reported subpop no. of observations seems wrong? and is subpop needed with replicate wgts.?
Date   Mon, 12 Feb 2007 11:28:09 -0600

Brent Fulton <fultonb@berkeley.edu> has a few questions regarding the
-subpop()- option on -svy:

> With Stata 9, I am using survey regression with the subpop command e.g.,
> 
> svy, subpop(var1): reg dep1 ind1
> 
> The regression result reports "Number of obs" and "Subpop. no. of obs".
> Based on running a few scenarios, the "Number of obs" includes all
> observations that have non-missing values for the regression variables,
> including the weights. This is as expected; however, the "Subpop. no. of
> obs" seems to include all observations that have a "1" for the subpop,
> including those observations that have missing values for the regression
> variables.
> 
> An actual example is below where I would have thought "Subpop. no. of obs"
> would have been 5329, not 5436. (This is a simple example. I am estimating
> several models with different sets of variables and am only able to find
> out how many observations Stata is really using by running an extra
> command such as: count if !missing(var1, var2, etc.).)
> 
> Lastly, I know if I am using the Taylor series approach to estimate
> parameter standard errors within a subpopulation, subpop is required
> (i.e., this is wrong: svy: reg dep1 ind1 if female==1). However, if I am
> using replicate weights, is subpop required?

-svy jackknife- was failing to update the variable that identifies the
supopulation sample when the prefixed estimation command drops observations
due to missing values (or other reasons).  

-svy linearized- and -svy brr- do not have this problem.

We should have -svy jackknife- fixed by the next ado-file update.

--Jeff
jpitblado@stata.com
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