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:

survival rate

mod.cox <- cph(formula = Surv(time, status) ~ age + weight,
               data=train, x= TRUE, y= TRUE, surv = TRUE)

Get the D_xy

v <- validate(mod.cox, dxy=TRUE, B=1000)
v

Compute C-index

Dxy = v[rownames(v)=="Dxy", colnames(v)=="index.corrected"]

The c-statistic according to the Dxy=2(c-0.5)

round(Dxy/2+0.5,3) #~0.5938927

So, I had C-index = 0.594. I wonder how can I get 95%CI from this?