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From |
Thomas Klausch <[email protected]> |

To |
[email protected] |

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 <[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: * 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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