# RE: st: baseline function estimates for stratified estimation

 From "Nick Cox" <[email protected]> To <[email protected]> Subject RE: st: baseline function estimates for stratified estimation Date Fri, 9 Aug 2002 11:32:44 +0100

```Roberto G. Gutierrez answered Christian Kaiser
>
> > 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.
>

As a footnote to Bobby's posting, check out -separate-.

. separate bsv_t, by(svars)

would give you a separate variable for each distinct stratum,
should you want them.

Nick
[email protected]

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