# EXERCISE 3.4
# =============

# Read leukemia data:
leukemia=read.table("http://folk.uio.no/borgan/abg-2008/data/leukemia.txt",header=T)


# We compute Kaplan-Meier estimates for the placebo 
# and 6_MP group and plot them in one figure 
#(Remember that you have to load the survival-library)

fit.3.4=survfit(Surv(time,status)~strata(treat),data=leukemia)
plot(fit.3.4, mark.time=F,xlim=c(0,25),xlab="Weeks",lty=1:2)
legend("topright",c("Placebo","6-MP"),lty=1:2)




# EXERCISE 3.7
# =============

# We compute Kaplan-Meier estimates for the placebo group
# with 95% log-minus-log transformed confidence limits:
fit.3.7=survfit(Surv(time,status)~1,data=leukemia,subset=(treat==1),conf.type="log-log")
plot(fit.3.7, mark.time=F,xlim=c(0,25),xlab="Weeks",lty=1:2)

# We may add a horizontal line at 0.50 to easier read off the
# estimated median with confidence intervals:
abline(0.5,0,lty=3)

# Note we obtain the estimated median with 
# confidence intervals by the command:
print(fit.3.7)