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Re: Re: st: random split


From   "Martin Weiss" <martin.weiss1@gmx.de>
To   <statalist@hsphsun2.harvard.edu>
Subject   Re: Re: st: random split
Date   Sun, 12 Apr 2009 23:44:34 +0200

<>

Very good call! I recommend that Galina use this solution to get an exact split...


HTH
Martin
_______________________
----- Original Message ----- From: "Glenn Goldsmith" <glenn.goldsmith@gmail.com>
To: <statalist@hsphsun2.harvard.edu>
Sent: Sunday, April 12, 2009 11:38 PM
Subject: RE: Re: st: random split


Hi,

If you want exactly 267 in the first group, won't the following achieve this
exactly?

 gen u = runiform()
 sort u
 gen split = _n <= 267

More generally (i.e. with _N!=800), you could use -ceil(_N/3)- or
-floor(_N/3)- to get 1/3, rounded up or down as desired.

HTH,

Glenn

"Martin Weiss" <martin.weiss1@gmx.de> wrote:

<>

"exactly a third of observations in the desired group"


How do you know that the split will be exact. Even leaving aside the
question whether ".33" is close enough to one third to warrant the
statement, the uniform number generator will still be noisy, i.e. the true
proportion will most likely be different from 1/3...




HTH
Martin

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