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cluster {survival}

Identify clusters.
Package: 
survival
Version: 
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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.

Details

The function's only action is semantic, to mark a variable as the cluster indicator. The resulting variance is what is known as the “working independence” variance in a GEE model. Note that one cannot use both a frailty term and a cluster term in the same model, the first is a mixed-effects approach to correlation and the second a GEE approach, and these don't mix.

Values

x

See Also

coxph, survreg

Examples

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

Documentation reproduced from R 3.0.1. License: GPL-2.