Practical exercise 1

 

In this exercise we will see how Nelson-Aalen plots may be used to study the effect of various covariates for the melanoma data given at the course web-page.

 

You may read the data into R by the command:

melanoma=read.table("http://www.uio.no/studier/emner/matnat/math/STK4080/h08/computing/melanoma.txt", header=T)

 

We will make Nelson-Aalen plots for the mortality from melanoma treating death from other causes as censoring. If we consider all patients, this may be performed by the commands

library(survival)

fit.mel0=survfit(Surv(lifetime,status==1)~1, data=melanoma, type="fl", error="ts", conf.type="plain")

plot(fit.mel0, fun="cumhaz", mark.time=F, xlab="Years after operation", ylab="Cumulative hazard")

 

a) Make Nelson-Aalen plots for males and females and interpret the plots.

 

b) Make Nelson-Aalen plots for patients with ulceration present and absent and interpret the results. (Ulceration is "present" if the surface of the tumor viewed in a microscope show signs of ulcers and "absent" otherwise.)

 

c) Make Nelson-Aalen plots for the three thickness groups 0-1 mm, 2-5 mm, 5+ mm and interpret the plots.