The following data set represents the survival times (in days from entry to a trial) for patients with stage 3 diffuse histiocytic lymphoma (from McKelvey et al., 1976, Cancer, 38, 1484-1493).

6, 19, 32, 42, 42, 43⁺, 94, 126⁺, 169⁺, 207, 211⁺, 227⁺, 253, 255⁺, 270⁺, 310⁺, 316⁺, 335⁺, 346⁺.

1. What does failure mean in the context of this study (provide examples)?
2. Compute the empirical reliability function using the Kaplan-Meier form of product limit estimator and estimate the reliability at 200 days.