Nonparametric tests for interval-censored failure time data

This paper discusses two sample nonparametric comparison of survival functions when only interval-censored failure time data are available. The problem considered often occurs in, for example, biological and medical studies such as medical follow-up studies and clinical trials. For the problem, we present and study several nonparametric test procedures that include methods based on both absolute and squared survival differences as well as simple survival differences. The presented tests provide alternatives to existing methods, most of which are rank-based tests and not sensitive to nonproportional or nonmonotone alternatives. Simulation studies are performed to evaluate and compare the proposed methods with existing methods and suggest that the proposed tests work well for nonmonotone alternatives as well as monotone alternatives. An illustrative example is presented.