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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 12:29:48 -0400

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

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