strata {survival} | R Documentation |
This is a special function used in the context of the Cox survival model. It identifies stratification variables when they appear on the right hand side of a formula.
strata(..., na.group=FALSE, shortlabel=FALSE)
... |
any number of variables. All must be the same length. |
na.group |
a logical variable, if TRUE , then missing values are treated as a
distinct level of each variable.
|
shortlabel |
if TRUE omit variable names from resulting
factor labels |
The result is identical to the interaction
function,
but for the labeling of the factors (strata
is more verbose).
a new factor, whose levels are all possible combinations of the factors supplied as arguments.
a<-factor(rep(1:3,4)) b<-factor(rep(1:4,3)) levels(strata(a)) levels(strata(a,b,shortlabel=TRUE)) coxph(Surv(futime, fustat) ~ age + strata(rx), data=ovarian)