data(TRACE)
TRACE$cluster <- sample(1:100,1878,replace=TRUE)
out1 <- km(Surv(time,status==9)~strata(vf,chf),data=TRACE)
out2 <- km(Surv(time,status==9)~strata(vf,chf)+cluster(cluster),data=TRACE)
par(mfrow=c(1,2))
bplot(out1,se=TRUE)
bplot(out2,se=TRUE)
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