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library(survival)
# the way a +cluster() term is handled in coxph has implications for update.
fit1 <- coxph(Surv(time, status) ~ age, cluster= inst, lung)
fit2 <- coxph(Surv(time, status) ~ age + cluster(inst), lung)
all.equal(fit1, fit2)
fit3 <- coxph(Surv(time, status) ~ age + sex + cluster(inst), lung)
test1 <- update(fit1, .~ .+ sex)
all.equal(test1, fit3)
# Gives a spurious warning message
test2 <- update(fit1, . ~ age + sex + cluster(inst), lung)
all.equal(test2, fit3)
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