1. A study of patients with stage I breast cancer is run to assess time to progression to stage II over an observation period of 15 years. Of interest is whether there is a difference in time to progression between women on two different chemotherapy regimens. Times to progression are measured in years from the time at which the chemotherapy regimen was initiated. SeeTable 11-26.

TABLE 11-26Years to Progression by Chemotherapy Regimen

Regimen 1	Regimen 2
Progression	No Progression	Progression	No Progression
2	12	9	11
6	14	4	14
7	13	7	13
3	11		9
4	15		14
	10		13
	8		6
	6		9
	9		7
	12

a. Estimate the survival functions (time to progression) for each chemotherapy regimen using the Kaplan Meier approach.

b. Test whether there is a significant difference in time to progression between treatment regimens using the log-rank test and a 5% level of significance.