Methods for comparing cumulative hazard functions in a semi-proportional hazard model.

Graphical methods based on the analysis of differences between log cumulative hazard functions are considered for a two-group semi-proportional hazard model which allows for interaction between treatments and covariates. Confidence procedures and test statistics that can be used to test for interaction and for main effects are developed. Their use is illustrated by applying them to the analysis of kidney transplant data from the University of California, San Francisco.