Practical exercise 4

In this exercise we will use Cox regression to study the effect of some 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 a univariate Cox regression analysis of each of covariates sex, tumor thickness, ulceration, and age at operation. For the numeric covariates you should consider whether they ought to be transformed or made into a categorical covariate by a suitable grouping.

b) Make a multivariate Cox regression analysis with all the covariates in question a. Reduce this model by removing covariates that are not significant (one at a time).