8.12 Survival Analysis

  • In many research settings, especially healthcare research, the response variable is the time to an event i.e. time to recovery, time to death, or time to relapse.

  • If the event has not occurred for an observation (either because the study ended or the patient dropped out) the observation is said to be censored.

  • The NCCTG Lung Cancer dataset in the survival package provides data on the survival times of patients with advanced lung cancer following treatment for up to 34 months.

  • The outcome for each patient is measured by two variables (1) time, survival time in days, (2) status, 1 = censored, 2 = dead.

  • Thus a patient with time = 305 & status = 2 lived 305 days following treatment. Another patient with time = 400 & status = 1, lived at least 400 days but then dropped out of the study. A patient with time = 1022 & status = 1, survived to the end of the study (34 months).