Consistent estimation of survival functions under uniform stochastic ordering; the k-sample case

Let S 1 , S 2 , ? , S k be survival functions of life distributions. They are said to be uniformly stochastically ordered, S 1 ? u s o S 2 ? u s o ? ? u s o S k , if S i / S i + 1 is a survival function for 1 ? i ? k - 1 . The nonparametric maximum likelihood estimators of the survival functions subject to this ordering constraint are known to be inconsistent in general. Consistent estimators were developed only for the case of k = 2 . In this paper we provide consistent estimators in the k -sample case, with and without censoring. In proving consistency, we needed to develop a new algorithm for isotonic regression that may be of independent interest.