strata {survival4} | R Documentation |
The result is identical to the interaction() function, but for the labeling of the factors (strata is more verbose).
strata(..., na.group=F)
... |
Any number of variables. All must be the same length. |
na.group |
if set to T, then missing values are treated as a distinct level of each variable. |
a new factor, whose levels are all possible combinations of the factors supplied as arguments.
data(ovarian) coxph(Surv(futime, fustat) ~ age + strata(rx))