This is a special function used in the context of the Cox model. It
identifies correlated groups of observations, and is used on the right hand
side of a formula.
USAGE:
cluster(x)
REQUIRED ARGUMENTS:
x
A character, factor, or numeric variable.
VALUE:
x
DETAILS:
The function's only action is semantic, to mark a variable as the
cluster indicator.
SEE ALSO:
,
.
EXAMPLES:
coxph(Surv(futime, fustat) ~ age + cluster(rx), data = ovarian)