Re: st: can the total sampling weights be applied to subsample analysis

[Steve Samuels <sjsamuels@gmail.com>]

The subpopulation observations receive the original sample weights.
These might not be appropriate for the subpopulation and can lead to
bias (See an example in Levy and Lemeshow, Sampling of Populations,
Wiley, 2008, pp. 147-148). There's not much that you can do about that
without external information about  the subpopulation.  I speculate
(but could be wrong!) that the bias arises when the probability of
being a subpopulation member is correlated with the original  weights.
If so, you can check for this bias by plotting the subpopulation
indicator against the weights with  -ksm-.   Or, more simply, just
check whether the distributions of the weights in the subpopulation
and its complement are different,

Steve

Steven Samuels
sjsamuels@gmail.com
18 Cantine's Island
Saugerties NY 12477
USA
Voice: 845-246-0774
Fax:    206-202-4783

On Fri, May 21, 2010 at 1:40 PM,  <jl591164@albany.edu> wrote:
> Thanks. That is acturally what i did, useing survey set first, then svy,
> subpop(). The subpop() option will use all cases in the calculation of
> standard errors, but only the subsample in the calculation of the point
> estimates. So, the total sampling weights will be used in the caculation
> of standard errors of subsample. I have a follow up question. How the
> total weights are applied to point estimates of the subsample by subpop()?
>
>
>> On Fri, May 21, 2010 at 11:32 AM,  <jl591164@albany.edu> wrote:
>>> My data provides a sampling weight to each id. But my study is based on
>>> a
>>> subsample of the data becasue i selected cases by two variables: age and
>>> type of placement. Can I still apply the whole sample weights to my
>>> subsample descriptive analysis? Thanks a lot.
>>
>> You should use the compete sample with -svy, subpop()- option. See
>> http://www.stata-journal.com/article.html?article=st0153.
>>

*
*   For searches and help try:
*   http://www.stata.com/help.cgi?search
*   http://www.stata.com/support/statalist/faq
*   http://www.ats.ucla.edu/stat/stata/