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


From   "Brent Fulton" <fultonb@berkeley.edu>
To   <statalist@hsphsun2.harvard.edu>, <jpitblado@stata.com>
Subject   RE: st: reported subpop no. of observations seems wrong? and is subpop needed with replicate wgts.?
Date   Mon, 12 Feb 2007 09:53:50 -0800

Thanks, Jeff, for your assistance. Just to clarify when using -svy
jackknife-, I assume Stata is estimating the parameters and SEs correctly on
the subpop, but it's just not reporting e(N_sub) correctly? Also, do you
know approximately when the update will be available?

Thanks,
Brent


-----Original Message-----
From: owner-statalist@hsphsun2.harvard.edu
[mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Jeff Pitblado,
StataCorp LP
Sent: Monday, February 12, 2007 9:28 AM
To: statalist@hsphsun2.harvard.edu
Subject: Re: st: reported subpop no. of observations seems wrong? and is
subpop needed with replicate wgts.?

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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