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Re: st: question on xtile using cutpoints


From   Maarten buis <maartenbuis@yahoo.co.uk>
To   stata list <statalist@hsphsun2.harvard.edu>
Subject   Re: st: question on xtile using cutpoints
Date   Wed, 22 Oct 2008 18:19:59 +0100 (BST)

--- Sharon Kane <spkane@uga.edu> wrote to me privately:

> Thanks Maarten, that does help some, but here is the rest of the
> specifics.  I have two choices for my cutpoints - 1. the original
> variable and 2. the variable containing quintiles 1-5.  When I select
> either of those as my cutpoints for the new variable, the results are
> strange.  Any further suggestions?

It is usually better to respond to the statalist for reasons discussed
in section 5 of the statalist FAQ.

A quick and dirty method is shown in the example below:

*------------- begin example -------------
// prepare the data
tempfile benchmark newdata

sysuse auto, clear
keep if foreign == 0
save `benchmark'

sysuse auto, clear
keep if foreign == 0
save `newdata'

// collect the cutvalues
use `benchmark', clear
_pctile mpg , nquantile(5)
return list

// apply these cutvalues to new data
use `newdata', clear
gen bench = .
forvalues i = 1/4 {
	replace bench = `r(r`i')' in `i'
}
list bench in 1/10
xtile newvar = mpg, cutpoints(bench)
tab newvar
tab mpg newvar
*------------- end example ----------------
(For more on how to use examples I sent to the Statalist, see
http://home.fsw.vu.nl/m.buis/stata/exampleFAQ.html )

Hope this helps,
Maarten


-----------------------------------------
Maarten L. Buis
Department of Social Research Methodology
Vrije Universiteit Amsterdam
Boelelaan 1081
1081 HV Amsterdam
The Netherlands

visiting address:
Buitenveldertselaan 3 (Metropolitan), room N515

+31 20 5986715

http://home.fsw.vu.nl/m.buis/
-----------------------------------------


      
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