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Identify strata variables.
Usage
strata(..., na.group=F)
Arguments
...
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.
Description
The result is identical to the interaction() function, but for the labeling of the factors (strata is more verbose).
Value
a new factor, whose levels are all possible combinations of the factors supplied as arguments.
See Also
coxph
Examples
coxph(Surv(futime, fustat) ~ age + strata(rx))