Practical exercise 3

In this exercise we will see how the Kaplan-Meier and Nelson-Aalen estimators in combination with the logrank test may be used to study the effect of various covariates for the melanoma data given at the course web-page. As we are interested in the mortality from malignant melanoma, we treat death form other causes as censored observations in the analysis.

a) Make Kaplan-Meier and Nelson-Aalen plots for each of the two genders, and test the difference using the logrank test. Discuss the results. Which additional information give the Nelson-Aalen plots compared to the Kaplan-Meier plots?

b) Repeat the analysis in a) for each of the three groups of tumor thickness: 0-1 mm, 2-5 mm, and 5+ mm.

c) Repeat the analysis in a) for ulceration. (Ulceration is present if the surface of the melanoma viewed in a microscope shows signs of ulcers and absent otherwise.)

d) Repeat the analysis in a) for age at operation. (Define suitable age groups using the command "cut".)