Sketch the survival functions for each group (obese and non-obese) using the results from Problem 5.

Problem 5

An observational cohort study is conducted to compare time to early failure in patients undergoing joint replacement surgery. Of specific interest is whether there is a difference in time to early failure between patients who are considered obese versus those who are not. The study is run for 40 weeks, and times to early joint failure, measured in weeks, are shown in Table 11–25 for participants classified as obese or not at the time of surgery.

a. Estimate the survival functions (time to early joint failure) for each group using the Kaplan–Meier approach.

b. Test whether there is a significant difference in time to early joint failure between obese and non-obese patients undergoing joint-replacement surgery using the log-rank test and a 5% level of significance.