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st: RE: re: Sample with weights


From   "Willard van Ooij" <w.van.ooij@marktmonitor.com>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: RE: re: Sample with weights
Date   Mon, 3 Oct 2005 10:15:54 +0200

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:Michael.Lacy@colostate.edu] 
Verzonden: zaterdag 1 oktober 2005 17:05
Aan: statalist@hsphsun2.harvard.edu
Onderwerp: st: re: Sample with weights


>
>Date: Fri, 30 Sep 2005 11:48:40 +0200
>From: "Willard van Ooij" <w.van.ooij@marktmonitor.com>
>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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