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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   Fri, 5 Oct 2007 14:30:36 +1000

Hi, thanks for the input.  .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. 
Sharon


-----Original Message-----
From: owner-statalist@hsphsun2.harvard.edu
[mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Maarten buis
Sent: Wednesday, 3 October 2007 5:25 PM
To: statalist@hsphsun2.harvard.edu
Subject: Re: st: St: How do fit a cox PH model for categorical outcome
variable with 3 levels in the same model


--- Sharon Johnatty <Sharon.Johnatty@qimr.edu.au> wrote:
> I've stset my data and I'm able to run cox models, no problem.  The 
> question is how do I obtain HRs for an outcome variable with three 
> levels, e.g. var_1_2  coded 0, 1, 2 in the same model, and obtain 
> separate estimates for 0 vs. 1 and 0 vs. 2.  Right now I'm able to do 
> this using  stcoxkm, by(var_1_2), then type stcox.  But Stata does not

> allow me to run an adjusted model in this way. Is there another way to

> fit a single model for a categorical variable with more than 2 levels 
> for both univariate and multivariate cox regression?

-stcox- is the Stata command for estimating a cox model, and it allows
multiple independent variables, and the output immediately gives you
hazard ratios. See the example below. The -xi:- prefix used in this
example is a convenience program that makes dummy variables from the
variable drug. So both _Idrug_2 and _Idrug_3 compare with _Idrug_1 (the
category left out, or the reference category).

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