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Re: st: get samples in Stata


From   sgsr100 <sgsr100@york.ac.uk>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: get samples in Stata
Date   Mon, 09 Feb 2004 15:27:57 +0000

thanks Nick,
Regards,
Sandra

Nick Cox wrote:
> 
> (can we go lower case please?)
> 
> You have a dataset.
> 
> You want to take a sample from part of it.
> 
> The key is to specify that part using -if-.
> 
> You later want to take a sample in another
> way.
> 
> The same is true. -if- specifies what you
> are sampling from.
> 
> If it's important that the samples don't
> overlap, as seems likely, that's to be
> included in the -if- condition second time
> around.
> 
> Whether you do this from first principles
> using random numbers directly or use
> a command like -sample- is secondary.
> 
> Nick
> n.j.cox@durham.ac.uk
> 
> sgsr100
> 
> > The think is I am trying to get random samples from a data set. I have
> > to use the traning and houldout data. But I have to get this samples
> > with the same criteria that the original data set was built.
> > In order to do this in a first stage I have to get a random
> > sample from
> > the primary units (it is composed of the group of housings ). In a
> > second stage I need to get another random sample from the secondary
> > units (it is composed of the group of households). Is the cluster
> > command useful for this?
> 
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