[R] How to use restricted cubic spline in survfit.cph function in "survival" package?

Zhiyuan Sun sam.d.sun at gmail.com
Thu Mar 6 04:51:55 CET 2014


Hello,

I used PBC data set included in the "survival" package to fit a cox
model. The model included a restricted cubic spline transformation on
age. Then I tried using "survfit" function to predict a survival curve
using the first row of the original data. I got an error message. The
R code and error message is below.

> require(survival)
> fit<-coxph(Surv(time,status==2)~rcs(age,4)+sex, data=pbc)
> id1<-pbc[1,]
> surv.id1<-survfit(fit,newdata=id1)
Error in rcspline.eval(x, nk = nknots, inclx = TRUE, pc = pc) :
  fewer than 6 non-missing observations with knots omitted


Can anyone provide any suggestions?

Thanks,
Zhiyuan



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