Cox model for cause-specific mortality for melanoma (all stages)

Use Cox regression to model the cause-specific survival of patients with skin melanoma (including all stages).

You may have to install the required packages the first time you use them. You can install a package by install.packages("package_of_interest") for each package you require.

Load the melanoma data and explore it.

(a)

First fit the model with sex as the only explanatory variable. Does there appear to be a difference in survival between males and females?

(b)

Is the effect of sex confounded by other factors (e.g. age, stage, subsite, period)? After controlling for potential confounders, does there still appear to a difference in survival between males and females?

(c)

Consider the hypothesis that there exists a class of melanomas where female sex hormones play a large role in the etiology. These hormone related cancers are diagnosed primarily in women and are, on average, less aggressive (i.e., prognosis is good). If such a hypothesis were true we might expect the effect of sex to be modified by age at diagnosis (e.g., pre versus post menopausal). Test whether this is the case.

(d)

Decide on a ‘most appropriate’ model for these data. Be sure to evaluate the proportional hazards assumption.