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

[jl591164@albany.edu]

Thanks a lot, Steve. That is very helpful.
Junqing

> 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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