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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