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

[jl591164@albany.edu]

Thanks, Steve. T-test and ranksum test indicate that the means of the
weights in the subpopulaiton and its complement are significantly
different. Does this mean that it is better not to apply the original
smaple weights to the subsample discriptive analysis? Thanks a lot.

Junqing


> 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.
>>>
>
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