The overall distribution of survival times for U.K. AIDS patients

Data on the survival times of 997 U.K. AIDS patients are analysed with the aim of deriving a simple form for the overall survival distribution. The exponential and Weibull distributions are modified to accommodate specific features of the data, in particular, the recording of survival times to the nearest month and the occurrence of a significant proportion of cases recorded as having zero time on study. The final model has a probability 0.08 of underlying survival time being zero and, given non-zero survival time, takes the form of an exponential distribution with mean of 14.95 months. The results are in close agreement with those of a study of New York City patients as well as the empirical data.