Dear all,
There is something I do not understand in fitting a cox regression
model in Splus.
Ok, I have a model fitted that way:
fit<-coxph(Surv(start,stop,event)~ "list of covariates")
I know I can collect back the y-coordinates of the cumulative baseline
hazard function that way:
cumsum(coxph.detail(fit)$hazard)
(and I can collect back the corresponding x-coordinates with:
coxph.detail(fit)$time)
What I do not understand is that we should also be able to collect this
through an estimate of the baseline survivor function, S0(t). This
function can be estimated that way:
S0t<-survfit(fit,list("here a list of values for the covariates
corresponding to the baseline hazard"))$surv
Then, since by definition H(t)=-log(S(t)), I was sure that
-log(S0t) should exactly correspond the cumulative baseline hazard
function, but this is not the case.
Can someone explain me where I'm wrong?
Thanks in advance for that.
Eric.
--
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Eric Wajnberg
Chair of the ESF Scientific programme on
Behavioural Ecology of Insect Parasitoids (BEPAR)
Associated Professor at the UQAM
(Universite du Quebec a Montréal)
I.N.R.A.
400 Route des Chappes, BP 167,
06903 Sophia Antipolis Cedex, France
Tel: (33-0) 4.92.38.64.47
Fax: (33-0) 4.92.38.65.57
e-mail: wajnberg@sophia.inra.fr
Web page: http://www.sophia.inra.fr/perso/wajnberg/
Editor-in-Chief of BioControl, Published by Springer.
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