Hi there, I have just constructed my own nomogram using cph function. Next, I compute C-index through D_xy value using the function validate of the package rms . It looks like:
mod.cox <- cph(formula = Surv(time, status) ~ age + weight, data=train, x= TRUE, y= TRUE, surv = TRUE)
v <- validate(mod.cox, dxy=TRUE, B=1000) v
Dxy = v[rownames(v)=="Dxy", colnames(v)=="index.corrected"]
So, I had C-index = 0.594. I wonder how can I get 95%CI from this?