source("http://192.38.117.59/~linearpredictors/datafiles/readCsl.R")
library(survival)

## ascites present?
csl$ascites <- csl$asc #ifelse(csl$asc != "0", 1, 0)
levels(csl$ascites) <- c("0","1","1")

## placebo as reference group
csl$tment <- relevel(csl$tment, ref = "1")

## no need to make dummy variables
full <- coxph(Surv(days, dc == 1) ~ sex + ascites:sex + ascites:sex:tment,
              data = csl)
summary(full)
noAscInt <- coxph(Surv(days, dc == 1) ~ sex + ascites:sex + sex:tment,
                  data = csl)
summary(noAscInt)
noSexInt <- coxph(Surv(days, dc == 1) ~ sex + ascites:sex + ascites:tment,
                  data = csl)
summary(noSexInt)
noInt <- coxph(Surv(days, dc == 1) ~ sex + ascites:sex + tment,
               data = csl)
summary(noInt)

## the LR tests can be carried out like this:
LR <- summary(full)$loglik[2]*2 - summary(noAscInt)$loglik[2]*2
## we drop 2 coefficients, so df=2
1-pchisq(LR, df=2)