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Re: st: Using stratified samples in STATA / giving weights


From   sjsamuels@gmail.com
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Using stratified samples in STATA / giving weights
Date   Tue, 8 Sep 2009 17:47:02 -0400

--
Thomas, I want to more directly answer part of your question.  I
believe you have two strata.  The basic sample weight for observations
in a stratum is :  N/n  where N is number of population elements in
the stratum, and n = the number in the sample.  However if you know
other information about the population other than that used to form
the strata , you can use it to improve the weights. See sections on
post-stratification in the books I referenced.

Steve


On Tue, Sep 8, 2009 at 12:29 PM, <sjsamuels@gmail.com> wrote:
> Thomas  Your knowledge about weights is faulty--weights are usually
>>1, for an observation's weight is the number of population members
> represented by the observation (the weight  can be non-integer).
> Weights <1 do arise, but not in the sample that you are describing.
> Before going any further.  I suggest that you read Sharon Lohr.
> Sampling: Design and Analysis, Duxbury, 1999).  Also, look at her
> section on sample size calculations.  The particular sample size
> calculation will depend on the purpose of your survey--whether
> descriptive or analytic.  If the latter than do not use the finite
> population correction.  If you know a lot of about your population,
> you can also apply post-stratification techniques.
>
> The book "Sampling of Populations" by Levy and Lemeshow (Wiley) has
> some Stata examples, although they are limited to descriptive samples.
>
> Regards,
>
> -Steve
>
>
> On Sat, Sep 5, 2009 at 11:26 AM, Thomas Klausch<thomas.klausch@gmail.com> wrote:
>> Dear list members,
>>
>> I am planning to survey a stratified sample from a relatively small finite
>> population of which I know the size. I am not too familiar with weighting
>> techniques and the STATA -svy- command family, which is why I write. Maybe
>> somebody can give useful advice.
>>
>> My popluation consists of size n=8800, with n=900 and n=7900 sized relevant
>> stratas. I decided to sample n=600 from each of the STRATAs since I am
>> particularly interested in estimates from the smaller strata.
>>
>> My knowledge about weighting tells me that this gives rise to weights of
>> approx. .20 for the small strata and approx. 1.80 for the large strata. In
>> SPSS I would know how to use the weights function, as there is only one.
>> STATA provides several weight options -fweight-, -pweight-, -aweight- and
>> -iweight-. I have tested in STATA that it gives the same estimates using
>> -iweight- than SPSS does using the WEIGHT BY command.
>>
>> My first question is if -iweight- is reasonable to use for my case when
>> estimating regression models (in particular logistic panel models).
>> My second question is whether there is a, maybe better, way to use the
>> options provided in the -svy- command family to specify the survey design.
>> maybe there is also a third way I do not know of.
>>
>> If anybody could give advice or further reference for detailed information
>> on -svy- I'd appreciate it a lot.
>>
>> Many thanks
>>
>> Thomas
>>
>> *
>> *   For searches and help try:
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>>
>
>
>
> --
> Steven Samuels
> sjsamuels@gmail.com
> 18 Cantine's Island
> Saugerties NY 12477
> USA
> 845-246-0774
>



-- 
Steven Samuels
sjsamuels@gmail.com
18 Cantine's Island
Saugerties NY 12477
USA
845-246-0774

*
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