he kidney data set is available in the survival library in R. It measures the time until a recurrent infection was observed in kidney dialysis patients. (a) Plot the log(-log) graphs of the estimates of the survival functions for the men and women in the study. Is there evidence that the proportional hazards model is not appropriate? (b) Plot the estimated survival function from coxph for an average female subject, and then the KM estimate using only the women in the study. Compare the two estimates. Does it look like the model gives a reasonable fit? (c) Use the cox.zph function to perform a test to see if the model is signif- icantly divergent from the proportional hazards model. Interpret the result. Do you think that we are justified in using the proportional hazards assumption in our modeling of the effect of sex? (d) Plot the Schoenfeld residuals. What do we observe