On Sat, Oct 1, 2011 at 2:31 PM, koshihaku <koshih...@gmail.com> wrote:
> Dear all,
> I am confused with the output of survfit.coxph.
> Someone said that the survival given by summary(survfit.coxph) is the
> baseline survival S_0, but some said that is the survival S=S_0^exp{beta*x}.
>
> Which one is correct?The baseline hazard as estimated in survfit.coxph is the hazard when all covariates are equal to the sample mean (or the stratum mean for a stratified model). The means that it is using are available in the $means component of the coxph object. It is not the hazard extrapolated to all covariates equal zero. The centering at the sample mean is done for three reasons 1/ it's computationally convenient 2/ it's numerically more stable 3/ it makes the baseline hazard more interpretable, since at least it is the hazard for a set of covariate values somewhere in the interior of your data. -thomas -- Thomas Lumley Professor of Biostatistics University of Auckland ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
