10.12 Exercises

10.12.1 Exercise

Using the above scripts, perform a univariable Kaplan Meier analysis to determine if ulcer influences overall survival. Hint: survival_object ~ ulcer.

Try modifying the plot produced (see Help for ggsurvplot). For example:

• Add in a median survival line: surv.median.line="hv"
• Alter the plot legend: legend.title = "Ulcer Present", legend.labs = c("No", "Yes")
• Change the y-axis to a percentage: ylab = "Probability of survival (%)", surv.scale = "percent"
• Display follow-up up to 10 years, and change the scale to 1 year: xlim = c(0,10), break.time.by = 1)

10.12.2 Exercise

Create a new CPH model, but now include the variable thickness as a variable.

• How would you interpret the output?
• Is it an independent predictor of overall survival in this model?
• Are CPH assumptions maintained?