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Re: st: random split


From   "Martin Weiss" <martin.weiss1@gmx.de>
To   <statalist@hsphsun2.harvard.edu>
Subject   Re: st: random split
Date   Sun, 12 Apr 2009 23:04:04 +0200

<>

To see my argument, run

****
//drop the thing
capt prog drop sim

//program definition
   program define sim // , rclass
       version 10.1
       drop _all
       set obs 800
   gen split = runiform()>.33
   cou if !split
   end

//simulation
   simulate N=r(N), reps(1000): sim

//get proportion instead of count
gen prop=N/800

//summarize results
su prop, d
kdensity prop, xli(0.33)
****


HTH
Martin
_______________________
----- Original Message ----- From: "Martin Weiss" <martin.weiss1@gmx.de>
To: <statalist@hsphsun2.harvard.edu>
Sent: Sunday, April 12, 2009 10:59 PM
Subject: Re: st: random split


<>

"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
_______________________
----- Original Message ----- From: "Rafal Raciborski" <rraciborski@gmail.com>
To: <statalist@hsphsun2.harvard.edu>
Sent: Sunday, April 12, 2009 10:54 PM
Subject: Re: st: random split


gen split = runiform()>.33

or a variation thereof to make sure you have exactly a third of
observations in the desired group




On Sun, Apr 12, 2009 at 4:48 PM, Galina Hayes <galina@uoguelph.ca> wrote:
Hello everyone,
I want to randomly split a data set of 800 or so observations into two groups, with 1/3rd of observations in the first group and 2/3rds in the second group, and am blanking on how to do this. Can anyone help?
Thanks,
Galina
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