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st: tvc option in stcox


From   "Sudhinaraset, May" <msudhina@jhsph.edu>
To   "statalist@hsphsun2.harvard.edu" <statalist@hsphsun2.harvard.edu>
Subject   st: tvc option in stcox
Date   Mon, 18 Apr 2011 14:58:29 -0400

Hello,

Someone else had asked the following question, and I am still a little unclear as to the answer, which I think is important: 

> (1)  How do you choose the best multiplier for the time-varying
> covariates (with -texp(exp)-)?  How do you know if ln(t) is better
> than t?

Given that you did the log-rank test for "drugclass" I assume that
those drugclass variables are binary, not continuous? The  -texp(exp)-
option is for continuous time varying covariates. In case of
categorical variables, I would do spell splitting with -stsplit-.

To ascertain the best multiplier for the time-varying covariates, is one way to look at Schoenfeld's residual with a lowess curve and fit of the data?

xi:stcox ruralnative ruraltourban urbantourban female alcohol i.wlthind3 i.schooljob i.famstruc, nolog noshow schoenfeld(sch*) scaledsch(sca*)
 
stphtest, log plot(ruralnative)

Are you looking for a linear relationship in this instance for the lowess curve to signify texp(_t) vs texp(ln(_t))? Are there other ways to graph this to see the best multiplier for time-varying covariates? 

Thanks,
May

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