Dear all, I tried to use "step" function to do model selection, but I got an error massage. What I don't understand is that data as data.frame worked well for my other programs, how come I cannot make it run this time. Could you please tell me how I can fix it? ***************************************************************************************************
all<-data.frame(z1,z2,z3)
fit.model.all<- coxph(Surv(t,cen) ~z1+z2+z3,data=all)
reg.model.all<-step(fit.model.all)
Start: AIC= 689.1 Surv(t, cen) ~ z1 + z2 + z3 Error in as.data.frame.default(data) : cannot coerce class "function" into a data.frame *************************************************************************************************** Thanks a lot! Jia