Mike, Nick and Svend,
Thanks very much for your suggestions. I will look into them and see
what works best for my case.
Willard
-----Oorspronkelijk bericht-----
Van: Mike Lacy [mailto:[email protected]]
Verzonden: zaterdag 1 oktober 2005 17:05
Aan: [email protected]
Onderwerp: st: re: Sample with weights
>
>Date: Fri, 30 Sep 2005 11:48:40 +0200
>From: "Willard van Ooij" <[email protected]>
>Subject: st: Sample with weights
>
>Dear statalisters,
>
>I have a population of company's. I want a sample from this population,
>but the probability of a company to be sampled has to be equivalent
>with the number of employees (let's call this "size").
>
>So I thought i could
>- -sample 10 [fweight=size]
>
>To get a 10 percent sample. But -sample- doesn't accept weights. A
>solution might be to expand the dataset with size, but then a company
>can get sampled several times if it has more than one employee, and I
>don't want that to happen. I think there must be a very simple
>solution, but I haven't been able to find it.
This is simple, produces a sample of exactly the desired size, and I
believe fulfills the condition of the probability of selection being
proportional to size . *Assume "Size" is the company size variable, and
M is the desired sample size gen ppsorder = uniform() * Size sort
ppsorder keep if _n <= M drop ppsorder
Yes, sorting the file is a bit clumsy, but this is presumably a one time
thing, not something appearing inside a loop.
Regards,
=-=-=-=-=-=-=-=-=-=-=-=-=
Mike Lacy
Fort Collins CO USA
(970) 491-6721 office
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