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

Value

x

See Also

coxph, Surv

Examples

data(kidney)
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)

data(rats)
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)