Consider the mouse carcinogenesis data of Appendix A (data set V). Compute the product limit (Kaplan-Meier) estimates (1.10) of the survivor function for the endpoint, reticulum cell sarcoma, for the control and germfree groups by: (a) Ignoring failures from thymic lymphoma and other causes (i.e., eliminate mice dying by these causes before carrying out calculations). (b) Regarding failure times from lymphoma or other causes as right censored. Comment on the relative merits of parts (a) and (b). (Hint: Try to understand what is being estimated in both cases.) On the basis of the survivor function plots, does the germ-free environment appear to reduce the risk of reticulum cell sarcoma ?