I am trying to understand difference in output between the following lines of code:
library(survival) summary(coxph(Surv(futime, fustat) ~ age + strata(rx), data=ovarian)) summary(coxph(Surv(futime, fustat) ~ age, data=ovarian))
What does adding
**Value** a new factor, whose levels are all possible combinations of the factors supplied as arguments.
What is the point to take all possible combinations of factor values, when they are mutually exclusive. What am I missing? Why example contains
strata(rx) i.e. only one factor, when explanation is talking about interaction of factors?