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 <[email protected]>:
> --
> 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, <[email protected]> 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<[email protected]> 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
>> [email protected]
>> 18 Cantine's Island
>> Saugerties NY 12477
>> USA
>> 845-246-0774
>>
>
>
>
> --
> Steven Samuels
> [email protected]
> 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:
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