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-