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RE: st: St: How to fit a cox PH model for categorical outcome variable with 3 levels in the same model


From   "Sharon Johnatty" <Sharon.Johnatty@qimr.edu.au>
To   <statalist@hsphsun2.harvard.edu>
Subject   RE: st: St: How to fit a cox PH model for categorical outcome variable with 3 levels in the same model
Date   Tue, 9 Oct 2007 11:43:37 +1000

Ok I don't know what I've done differently, but coding with 0, 1, 2
works!!  For some reason it did not before but....gremlins are in my
computer (or my head.....)

Thanks so much for your help
Sharon

-----Original Message-----
From: owner-statalist@hsphsun2.harvard.edu
[mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Maarten buis
Sent: Friday, 5 October 2007 5:17 PM
To: statalist@hsphsun2.harvard.edu
Subject: RE: st: St: How to fit a cox PH model for categorical outcome
variable with 3 levels in the same model


--- Sharon Johnatty <Sharon.Johnatty@qimr.edu.au> wrote:
> xi: stcox works, but only if variable is coded 1, 2 or 3. It doesn't 
> work if the variable is coded 0, 1, 2.

That is very very strange. -xi- just looks at distinct values, not their
actual contents, so it should work with any coding. In the example below
I have changed the coding of drug to 0, 1, 2, and it works. So, could
you tell us a bit more about what is not working, so we can solve the
problem. 

*------------------ begin example ---------------
sysuse cancer, clear
stset studytim, failure(died)

/*Change the coding to 0, 1, 2*/
replace drug = drug -1 

xi: stcox i.drug age
*------------------ 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 Z434

+31 20 5986715

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


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