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Re: st: weights in pooled repeated cross sections


From   Steven Samuels <sjsamuels@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: weights in pooled repeated cross sections
Date   Wed, 28 Sep 2011 09:12:00 -0400

I think that the notion of an "average population" is not only useful but often unavoidable, even for single year surveys.   Many of these are conducted over a period of months, sometimes, for continuous surveys, over 12 months. As such, the population represented is the "average population" for the time period.

Austin Nichols once suggested that the proper denominator  for multi-year surveys should be not persons, but "person-years". This is just another version of the "average population" over the for the survey period. 

Even more: many national yearly surveys provide modified weights so that population frequencies of important characteristics (age, gender, ethnic group) match the frequencies in recent censuses.





Steve

 



On Sep 28, 2011, at 4:36 AM, Ivica Rubil wrote:

Steve, Cameron:

According to the paper that Cameron suggested me to read: 
" It   is  not   a lways  necessary  to  adjust
the  weights  when pooling  the  dat a .
When   weights   are   adjusted ,   the
assumption   is  that  they  are  being
adjusted  to   properly   represent   a
population.  The problem is that when
we ight s   f rom di ff e r ent   t ime  pe r iods
a r e   combined,   the   r e sul t ing we ight s
do not represent the current population,
but rather, an average population that
does not exist.  Consequently, creating
tot a l s  wi th  a   combined  f i l e  may not
b e   a p p r o p r i a t e ,  wh e t h e r   o r   n o t   t h e
we ight s   a r e   adjus t ed.    On  the  othe r
hand,   r a t ios ,  propor t ions   and me ans
can be regarded as useful statistics when
cons ide r ed  a s  pe r iod  e s t ima t e s .    For
these types of statistics, the results using
the original weights or the weights that
have  be en  adjus t ed us ing  a   common
factor 1/k (k= # of datasets combined) will give the same result.  
This a l so holds   for   r e gr e s s i o n   p a r a m e t e r s ,
whe r e  we ight s   a r e  us ed  in  the  mode l
in order to take the survey design into
account rather than to make estimates
for   some   f ini t e  popul a t ion.


--
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 Cameron
McIntosh
Sent: 28. rujan 2011 0:17
To: STATA LIST
Subject: RE: st: weights in pooled repeated cross sections

Ivaca,
Strategies for dealing with your type of situation are dealt with in:
Thomas, S., & Wannell, B. (2009). Combining cycles of the Canadian
Community Health Survey. Health Reports,
20(1).http://www.statcan.gc.ca/pub/82-003-x/2009001/article/10795-eng.pd
f
Cam
----------------------------------------
> Subject: Re: st: weights in pooled repeated cross sections
> From: sjsamuels@gmail.com
> Date: Tue, 27 Sep 2011 17:30:10 -0400
> To: statalist@hsphsun2.harvard.edu
> 
> 
> Thanks, Nick. I missed that part of Ivica's question.
> 
> 
> To Ivica, I would say: you can usually find a description of the study
design and variables in the study manuals and reports. For example, the
2008 Survey is described in www.dzs.hr/Eng/Publication/2009/SI-1400.pdf
and contains the statement:
> 
> "In the year 2008, the Household Budget Survey sample was selected in
two stages. In the first one there were 467 segments selected (segments
are groups of neighbouring enumeration areas) out of segments previously
selected for the 2008 Labour Force Survey. In the second stage, out of
each of selected segments, 10 dwellings, occupied by private households,
were selected, which were not previously selected into the 2008 Labour
Force Survey. Thus, 4 670 dwellings occupied by private households were
selected. At each selected occupied dwelling all private households were
interviewed."
> 
> This says nothing about previous years, but the answer might lie in
reports about the Labor Force Survey. You should contact the Central
Bureau of Statistics. If they have a web site, the reports might be
there.
> 
> A survey analysis which does not account for the design
variables-strata, PSUs- will produce standard errors and p-values which
are too small, usually much too small. Such an analysis assumes that the
observations are independent, whereas the effective sample size is more
the number of PSUs than the number of households.
> 
> 
> Regards,
> 
> Steve
> 
> 
> 
> On Sep 27, 2011, at 4:35 PM, Nick Cox 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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