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st: random sample selection


From   "raoul reulen" <r.c.reulen@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   st: random sample selection
Date   Tue, 1 Apr 2008 13:38:48 +0100

Hi Statalisters,

I am trying to get a random sample of 40 subjects from a dataset of a
few hundred subject. This is what I did:

.set seed 12345
.gen random = uniform()
.sort random, stable
.drop if _n>40


For various reasons, it might be that some subjects in the sample are
not suitable for selection and I want to exclude them from the sample
and from the overall dataset.

So I selected another sample, however, when I did that other subjects
were selected as well.

.drop if id == 890800  //subject that wasn't suitable dropped
.set seed 12345
.gen random = uniform()
.sort random, stable
.drop if _n>40


What I want is to keep the original 39 subjects as in the old sample
in  and just replace the subject that wasn't suitable. Any suggestions
would be appreciated.

Many thanks.

Raoul




-- 
-------------------------------------------------------
Raoul C. Reulen
Cancer Research UK Training Fellow
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