Survival Analyses of Radiated Animals Incorporating Competing Risks andCovariates

摘要

The United States Air Force has been interested in studying the effect ofdifferent types of radiation encountered by its personnel in space. A study was, therefore, conducted at the USAF School of Aerospace Medicine, Brooks Air Force, Texas with rhesus monkeys as experimental subjects. These subjects were exposed to different types of radiation such as: (1) electromagnetic radiation; (2) electrons; (3) protons; and (4) nuclei of elements of higher numbers with different amount of radiation. These subjects were followed over a period of 338 months. In this paper an interesting problem related to health and radiation has been addressed. The effects of radiation, taking into account the cause of death (cancer or heart disease) along with the covariates such as sex, age, type of exposure, does, are examined. A general log-linear hazard model approach is studied. The model estimates the cause specific hazard rates, assuming piecewise exponential distribution, and exhibits the survival function for each of the covariate groups and the probability of death due to each cause. A data set called 'Delayed Bio-Effects Colony,' of radiated animals, is analysed and some conclusions are drawn. Overall the study has brough out the effect of high and how does of radiation on both the male and female groups. The procedure presented in the paper distinguishes between time varying hazards. Thus the methodology may be useful for other survival related environmental problems, be this with regard to animal or human survival. Thus, the paper could contribute to its more widespread use.