Survival analyses in twin studies and matched pair experiments

Several models for paired failure time data are considered. It is assumed that the effects of certain risk factors or treatments are of primary interest and such effects are written as regression parameters in a proportional hazards model. Techniques based on marginally sufficient statistics are proposed for their estimation. Efficiency comparisons are made among estimates based on the suggested models and special attention is given to the study of bias and efficiency in the presence of censoring. Some comparisons are made between the models and analyses presented here and analyses based on study period survival and a binary logistic model for regression parameters.