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Re: st: creating variable from svy: proportion


From   Steve Samuels <sjsamuels@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: creating variable from svy: proportion
Date   Mon, 3 May 2010 12:26:32 -0400

You should be fine with these weights. Problems can arise if the
original probability weights are post-stratified or otherwise "raked"
so that sample estimates better match population totals. These
post-stratified weights might not  be appropriate for individual
cooperatives (or for sub-populations in general). See Levy and
Lemeshow, Sampling of Populations, 4th Ed, 2008, page 149. I would
have suggested that you use the original probability weights, if
available:
new_weight = (1/prob sel coop)x (1/prob sel popcode) x (1/ prob sel individual).

With these weights,

svy: total isb17, over(dccode)

would give wrong estimates of totals, because the weight includes a
factor for sampling of the cooperative. So, if the probability of
selecting a coop was 1/10, the total estimate for that coop would be
inflated 10-fold. You only need the product of the last two factors

However estimates of proportions and other means will be unbiased,
because the extra coop selection factor (10, in the example) cancels
out of the numerator (estimate of number of individuals with isb17=1)
and denominator (estimate of number of individuals in the coop).

Steve

On Mon, May 3, 2010 at 11:52 AM, Guy Grossman <guygrossman1@gmail.com> wrote:
> weights were constructed by calculating the inverse of the probability
> of being included in the sample (basically 1/(multiplying probability
> in each of the three sampling stages)). For which constructions you
> believe pweights would be biased? what re-weighting method do you
> propose?
>
> Guy
>
> On Mon, May 3, 2010 at 11:43 AM, Steve Samuels <sjsamuels@gmail.com> wrote:
>> How were the weights constructed, Guy?   For some constructions, the
>> estimates for individual cooperatives could be quite biased, and
>> re-weighting might be necessary.
>>
>> Steve
>>
>> On Mon, May 3, 2010 at 10:20 AM, Guy Grossman <guygrossman1@gmail.com> wrote:
>>> Dear Stata listers,
>>>
>>> forgive me for posting such a basic question. I am using Stata 10.1 to
>>> analyze an original stratified three-stage cluster sample survey in
>>> which observation are farmers (individuals) sampled from groups
>>> (pocode) themselves sampled from larger farmer cooperatives (dccode).
>>> isb17 is a dummy variable measured at the individual level. I am
>>> trying to create a variable at the PSUs level (dccode), which is the
>>> proportion of farmers in the cooperative that have  isb17==1.  I am
>>> reluctant to use the collapse command given the survey design.
>>>
>>> svyset dccode [pw= pweight], strata (strata) fpc(fpc1) || pocode,
>>> fpc(npos) || _n, fpc(popop)
>>> svy: proportion isb17, over(dccode)
>>>
>>> What I am failing to do, is to take the e(b) from ereturn and generate
>>> a variable that represents isb17==1 at the dccode level.
>>> Help would be highly appreciated.
>>>
>>> Cheers,
>>> Guy
>>>
>>> *
>>> *   For searches and help try:
>>> *   http://www.stata.com/help.cgi?search
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>>>
>>
>>
>>
>> --
>> Steven Samuels
>> sjsamuels@gmail.com
>> 18 Cantine's Island
>> Saugerties NY 12477
>> USA
>> Voice: 845-246-0774
>> Fax:    206-202-4783
>>
>> *
>> *   For searches and help try:
>> *   http://www.stata.com/help.cgi?search
>> *   http://www.stata.com/support/statalist/faq
>> *   http://www.ats.ucla.edu/stat/stata/
>>
>
>
>
> --
> Guy Grossman | PhD Candidate - Columbia University | Political Science
> Department | IGERT International Development and Globalization Fellow
> |  (+1917) 664-6946 | gsg2102@columbia.edu  |  skype: gugrossman |
> http://www.columbia.edu/~gsg2102/ |
>
> *
> *   For searches and help try:
> *   http://www.stata.com/help.cgi?search
> *   http://www.stata.com/support/statalist/faq
> *   http://www.ats.ucla.edu/stat/stata/
>



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

*
*   For searches and help try:
*   http://www.stata.com/help.cgi?search
*   http://www.stata.com/support/statalist/faq
*   http://www.ats.ucla.edu/stat/stata/


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