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


From   Steve Samuels <sjsamuels@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: can the total sampling weights be applied to subsample analysis
Date   Mon, 24 May 2010 16:21:57 -0400

No, it just means, if anything, that you should not make much of small
differences..  In the admittedly artificial example in L&L's book, the
estimate of the subpopulation mean was $11.52, compared to the true
value of $11.60.   I can  think of examples where a difference in the
distribution of weights would be expected and would not lead to bias.

No  sampling text advises against using the sample weights, and I
would use them. Note that if a subpopulation size is <20, then the
standard errors that Stata reports will be untrustworthy.

Steve

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



On Mon, May 24, 2010 at 3:37 PM,  <jl591164@albany.edu> wrote:
> 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.

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

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