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Re: st: baseline function estimates for stratified estimation


From   rgutierrez@stata.com (Roberto G. Gutierrez, StataCorp.)
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: baseline function estimates for stratified estimation
Date   Thu, 08 Aug 2002 16:36:34 -0500

Christian Kaiser <Christian.Kaiser@unisg.ch> asks:

> I did some Cox prop. hazard estimations using the strata option. According
> to the reference manual, estimates of the baseline functions for each
> stratum should have been stored. However, when I type stcox xvars, strata
> (svars) basechazard(bch) basesurv(bsv) I only get the two vectors bch and
> bsv. As far as I understand I should get one of these vectors for each value
> of my svars. How can I retreive the single vectors?

The estimated baseline functions are always generated as single variables.
When you stratify, the variable containing the estimated baseline function 
is "stratified" as well.  The estimated function values for each stratum are
contained within the one generated variable and are organized to mirror the
organization of your stratification variable.

So, for example, if your variable -svars- consists of the values 1, 2, and 
3, then 

   . list bsv _t if svars == 1

will list the estimated baseline survival function for the "first" strata,

   . list bsv _t if svars == 2

for the second strata, etc.

If this seems a bit sparse on information recall that the estimated cumulative
hazard and survival function are step functions where the steps occur only at
the observed failure times.  Thus, even when you stratify you only need a
single variable to contain all the required information.

--Bobby
rgutierrez@stata.com
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