Extra exercise 3

In this exercise we will consider the melanoma data discussed at the lectures. 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 plots for each of the two genders, and test the difference using the logrank test. Discuss the results.

 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) Make a univariate Cox regression analysis of each of the covariates sex, tumor thickness and? ulceration. For the numeric covariate tumor thickness you should consider whether you ought to use the original version "thickn", the log-transformed version "logthick", or the grouped version "grthick" (as a factor). Interpret the results and compare with the results in a-c.

e) Make a multivariate Cox regression analysis with the covariates mentioned in question d. Interpret the fitted model.