cluster               package:survival               R Documentation

Identify Clusters

Description:

     This is a special function used in the context of survival models.
      It identifies correlated groups of observations, and is used on
     the right hand side of a formula.  Using 'cluster()' in a formula
     implies that robust sandwich variance estimators are desired.

Usage:

     cluster(x)

Arguments:

       x: A character, factor, or numeric variable. 

Value:

     'x'

See Also:

     'coxph', 'Surv'

Examples:

     frailty.model <- coxph(Surv(time, status)~ age + sex + disease + frailty(id), kidney)
     marginal.model <- coxph(Surv(time, status)~ age + sex + disease+cluster(id), kidney)
     summary(frailty.model)
     summary(marginal.model)

     frailty.model <- survreg(Surv(time, status) ~ rx +  frailty(litter), rats )
     marginal.model <- survreg(Surv(time, status) ~ rx +  cluster(litter), rats )
     summary(frailty.model)
     summary(marginal.model)

