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Re: st: stcurve and multiple strata


From   Maarten buis <maartenbuis@yahoo.co.uk>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: stcurve and multiple strata
Date   Thu, 11 Sep 2008 13:06:24 +0100 (BST)

--- moleps islon <moleps2@gmail.com> wrote:
> Right now my cox model looks like this:
> 
> xi:stcox a b d i.c, basesurv(e)
> 
> I need to make survival graphs adjusted for the other variables for
> the individual i.c categories. I tried
> 
> stcurve, survival at1(_Ic_2=1) at2(_Ic_3=1) etc, etc but somehow I 
> can't find my first expansion term anywhere. Ideas?

That will not work: -xi- creates a set of dummies, -stcurve- set
variables not mentioned in -at#()- at the mean, so just saying _Ic_2=1
will not properly identify the second group, as _Ic_3 is set at the
mean, but should be set at 0. The reference category is identified by
both variables set equal to 0. 

*----------- begin example ------------
sysuse cancer, clear
stset studytim, failure(died)
xi: stcox i.drug age, basesurv(e)
stcurve, surv ///
     at1(_Idrug_2=0 _Idrug_3=0) ///
     at2(_Idrug_2=1 _Idrug_3=0) ///
     at3(_Idrug_2=0 _Idrug_3=1) 	
*----------- 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 )

Also see:
http://www.ats.ucla.edu/stat/stata/faq/dummy.htm

-- 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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