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# Re: st: weights in pooled repeated cross sections

 From Steven Samuels To statalist@hsphsun2.harvard.edu Subject Re: st: weights in pooled repeated cross sections Date Tue, 27 Sep 2011 17:40:06 -0400

```Fernando-

If, say, 90 PSUs repeated over four years, an analysis which ignored this would count them as 360 PSUs. The consequence would be standard errors and p-values that are too small.

By the way, I have ignored this issue in past posts to Statalist,  which recommended that "years" could (always) be crossed with the original strata to form new super-strata.  I apologize for this incorrect advice.

Steve

On Sep 27, 2011, at 4:37 PM, Fernando Rios Avila wrote:

Hi Steven,
Since it seems you have experience with this kind of data, i wonder if
you know if there is any particular consequence of pooling and using
the weights as you mention when each individual survey is not
statistically independent from each other, meaning that some Primary
sample units may appear more than once through the different surveys,
while others wont.
Thanks!

On Tue, Sep 27, 2011 at 4:35 PM, Nick Cox <njcoxstata@gmail.com> wrote:
> PSUs are primary survey units.
>
> Nick
>
> On Tue, Sep 27, 2011 at 9:32 PM, Steven Samuels <sjsamuels@gmail.com> wrote:
>>
>> 1. Pool
>> 2. Divide weights by four (would affect only totals, but still a good idea)
>> 3. -svyset- the whole thing.
>>
>>
>> Steve
>>
>> On Sep 27, 2011, at 10:40 AM, Ivica Rubil wrote:
>>
>> so, you're saying I just pool the 4 datasets, divide the weights by 4,
>> and apply -svyset- to the pooled dataset? Or should I rather use
>> -svyset- for each of the 4 datasets, pool them in one, and then divide
>> the weights by 4?
>> Further, sorry for bothering you: what are PSUs? How do I check if they
>> change form year to year?
>>
>> --
>> Ivica Rubil
>> Ekonomski institut / The Institute of Economics, Zagreb
>> Trg J. F. Kennedyja 7, 10 000 Zagreb, Croatia
>> tel. +385-1-2362-269
>> fax. +385-1-2335-165
>> irubil@eizg.hr
>> www.eizg.hr
>>
>>
>> -----Original Message-----
>> From: owner-statalist@hsphsun2.harvard.edu
>> [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Steven
>> Samuels
>> Sent: 27. rujan 2011 15:51
>> To: statalist@hsphsun2.harvard.edu
>> Subject: Re: st: weights in pooled repeated cross sections
>>
>>
>> Ivica-
>> You can use the individual weights, Ivica, but divide by 4 so that they
>> sum to the average population total over the four years
>>
>> You still have to write the rest of the -svyset- command.  If the PSUs
>> did not change over the four years, then treat the pooled sample as one
>> large sample, and use the same -svyset- statement that you would use for
>> a single year.  If some PSUs changed you will have to do some stratum
>> recoding. For an example see
>> http://www.cdc.gov/nchs/ppt/nchs2010/46_Moriarity.ppt
>>
>> Steve
>>
>> On Sep 26, 2011, at 12:03 PM, Ivica Rubil wrote:
>>
>> Dear all,
>>
>> I am trying to pool four repeated cross-sections of Croatian Hpusehold
>> Budget Survey.
>> For each year that I want to pool, I have sampling weights for each
>> observation (both household and person).
>> My questions are: What should I do with the weights once I pool the four
>> datasets? Is it wrong to use
>> dataset-specific weights in the pooled dataset and just run estimation
>> commands with the weight option, if
>> available? I am confused. Please, help.
>>
>
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