Statalist


[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

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


From   Thomas Klausch <thomas.klausch@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Using stratified samples in STATA / giving weights
Date   Wed, 9 Sep 2009 10:21:02 +0200

Hi Steve,

Many thanks for your advice. I will check out the references you gave.

I was suprised about the weighting that you describe, though. As far
as I was aware a proper weight is computed as

weight= % in population / % in sample

For my example (large stratum) I would then have

% in population = 7900/8800=.898
% in sample = 600/1200=.5

weight= .898/.5 =1.797

The same follows for the small stratum.

Now you suggest N/n= 7900/600=13.17 ?

Is that correct? I wouldn't see the point yet...

Maybe you or somebody else also knows the answer to my question,
whether in STATA -iweight- option is the correct one to use.

Many thanks.

Best
Thomas




2009/9/8  <sjsamuels@gmail.com>:
> --
> 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:
>>> *   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
>> 845-246-0774
>>
>
>
>
> --
> Steven Samuels
> sjsamuels@gmail.com
> 18 Cantine's Island
> Saugerties NY 12477
> USA
> 845-246-0774
>
> *
> *   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/
>

*
*   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/



© Copyright 1996–2014 StataCorp LP   |   Terms of use   |   Privacy   |   Contact us   |   What's new   |   Site index