The data in the table are from Freireich et al. (1963) and show the result of a study where children with leukemia are treated with a drug (6-MP) to prevent relapse, and where this treatment is...

The data in the table are from Freireich et al. (1963) and show the result of a study where children with leukemia are treated with a drug (6-MP) to prevent relapse, and where this treatment is compared with placebo. The numbers in the table are remission lengths in weeks; a * indicates a censored observation.

a) Compute the Nelson-Aalen estimates for the 6-MP group and for the placebo group.

b) Plot both Nelson-Aalen estimates in the same figure. What can you learn from the plots?