[R] [newbie] Cox Baseline Hazard
gb at stat.umu.se
Fri Feb 23 09:17:03 CET 2001
On Fri, 23 Feb 2001, Meles MELES wrote:
> I must have a vocabulary problem.
> I've tryed the method you gave me and I get a Cumulative Hazard for my
> But, what I'm looking for is the Baseline Hazard (I don't know if the
> term is appropriate).
> If I consider a cox model for the intantaneous risk of death:
> h(t,Z)=h0(t)exp(b'Z), what I'm looking for is H0(t).
> What I get with the surfit() methot is H(t).
> I might be completly wrong, but when I compute my data in SPSS, I get a
> Cumulative Baseline Hazard of 0.062, in R, with the surfit way, I get
> 0.33, which correspond in the SPSS result to the Cumulative Hazard.
> I hope that what i'm writing is not too fuzzy.
> I hope my questions are not too boring :-)
I think the problem here is that what Thomas and Peter call the
"baseline hazard" actually is calculated at the mean values of
the covariates. You can get what you want by using the "newdata"
parameter in survfit. Try
fit <- coxph( Surv(futime,fustat)~resid.ds+rx+ecog.ps,data=ovarian)
base <- data.frame(age=0, resid.ds=0, rx = 0, ecog.ps = 0)
ss <- survfit(fit)
ss1 <- survfit(fit, newdata = base)
par(mfrow = c(2, 1))
plot(ss, fun = "cumhaz")
plot(ss1, fun = "cumhaz")
and you see the difference.
Göran Broström tel: +46 90 786 5223
professor fax: +46 90 786 6614
Department of Statistics http://www.stat.umu.se/egna/gb/
SE-90187 Umeå, Sweden e-mail: gb at stat.umu.se
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