Using the survival package in R I am trying to calculate 95% confidence interval (CI) of the proportional hazards model coefficient. Normally this is pretty simple to do with the survival package.
> confint(cch(Surv(time, event) ~ a + b + c, ...)) 2.5 % 97.5 % a -0.4216482 0.1225872 b 0.2624281 1.3339170 c 0.3344311 1.2224415
However when I try to do this in a univariable setting, the confint function fails to return anything, except a matrix with no rows.
> confint(cch(Surv(time, event) ~ a, ...)) 2.5 % 97.5 %
Is this a bug in R or am I missing something else? If this is a bug how can I calculate these CIs 'by hand'?