tt <- function(x) {
obrien <- function(x) {
r <- rank(x)
(r - 0.5)/(0.5 + length(r) - r)
}
unlist(tapply(x, riskset, obrien))
}
hi, i am newer in R. when dealing with a survival data, i have found the
variable progression was not met the PH assumption.the picture show the
residual agaist time.So i use Cox model for time-depandent varibles. i use
the default tt in function coxph,but when i use tt in
"f<-cph(Surv(os$Stime,os$Status==1)~Metastasis+Surgery+Post.chem.
+Age+tt(Progression)+ ALP, data=os, x=T, y=T, surv=TRUE, time.inc=60)",it
didn't work. i don't kown what the arg"riskset" is .i beg your help . can you
help me write down a appropriate tt expression to let me use in cph. thanks.
Zhongxin
Dong
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