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


From   Maarten buis <maartenbuis@yahoo.co.uk>
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
Date   Wed, 3 Oct 2007 08:24:34 +0100 (BST)

--- 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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