Rahul Bhattacharya

On a class of optimal covariate-adjusted response adaptive designs for survival outcomes

A class of optimal covariate-adjusted response adaptive procedures is developed for phase III clinical trials when the treatment response is a survival time and there is random censoring. The basic aim is to develop an allocation design by combining the ethical aspects with statistical precision in a reasonable way under the presence of covariate information. Considering minimisation of total hazards as the ethical requirement, the proposed procedure is assessed in terms of the assignment to the better treatment and the efficiency (i.e. power) to detect a small departure in treatment effectiveness. The applicability of the proposed methodology is also illustrated using a real data set.

A randomized two stage allocation for continuous response clinical trials

A randomized two treatment allocation design, conducted in two stages, is proposed for a class of continuous response trials. Patients are assigned to each treatment in equal numbers in the first stage and p value of a test of equality of treatment effects based on these data is used to determine the assignment probability of second stage patients. Relevant properties of the proposed allocation design are investigated and compared with suitable competitors.

On an ethical cum optimal adaptive allocation design

Abstract In the present work, we formulate a two-treatment single period two-stage adaptive allocation design for achieving larger allocation proportion to the better treatment arm in the course of the trial with increased precision of the parameter estimator. We examine some properties of the proposed rule and compare it with some of the existing allocation rules and report substantial gain in efficiency with a considerably larger number of allocations to the better treatment even for moderate sample sizes.

A covariate-adjusted response-adaptive allocation in clinical trials for a general class of responses

A class of covariate-adjusted adaptive allocation procedures is developed for a general class of responses with an aim to satisfy relevant clinical requirements. Some exact and asymptotic properties of the procedures, proposed and a reasonable competitor, are studied and compared under the presence of treatment-covariate interaction.

Estimation in a Two-Stage Procedure for Failure Censored Model

A reliability setting is considered for comparing two competing equipments based on a fixed number of observations. A two stage failure censored design is proposed in which a preassigned number of items are randomised equally at the first stage and the better items are examined exclusively at the end of the second stage. Here at each stage, we consider type II censoring (see e.g. Miller (1981)) . That is, observations are made upto a common prefixed proportion of failures at each stage. For exponential responses, the exact bias and variance of the estimated failure rate difference at the end of the trial are derived. Competitors of the proposed procedure are also suggested. Some asymptotics related to all these procedures are also obtained.

An Optimal Three Treatment Allocation for Binary Treatment Responses

ABSTRACT An optimal target proportion is derived balancing between the needs of clinician and statistician considering a general criterion and binary treatment outcome. A response-adaptive procedure based on this optimal proportion is developed and the associated limiting results are derived. In addition, the proposed procedure is compared with the existing competitors.

A two-stage adaptive allocation design for survival outcome with informative censoring

An adaptive two-stage allocation design is developed for survival responses subject to independent informative censoring. The asymptotic p value of a score test related to a hypothesis of treatment effectiveness is used to set the assignment probability of the second stage. Several characteristics of the design and the follow-up inference are studied, both numerically and theoretically, and are compared with those of an existing competitor. Applicability of the proposed design is also illustrated through a real data.

A response adaptive design for ordinal categorical responses

ABSTRACT A two treatment response adaptive design is developed for phase III clinical trials with ordinal categorical treatment outcome using Goodman-Kruskal measure of association. Properties of the proposed design are studied both empirically and theoretically and the acceptability is further illustrated using two real data-sets; one from a clinical trial with trauma patients and the other from a trial with patients having rheumatoid arthritis.

A class of Covariate-Adjusted Response-Adaptive Allocation Designs for Multitreatment Binary Response Trials

ABSTRACT A class of covariate-adjusted response-adaptive randomization procedures is developed for binary treatment outcomes in a phase III clinical trial set up involving multiple treatments. The target allocation is developed by combining the ethical aspects with statistical precision under the existence of treatment covariate interaction. Relevant measures of the performance for the proposed allocation designs are studied and compared.

A multi-treatment two stage adaptive allocation for survival outcomes

ABSTRACT A multi-treatment two stage adaptive allocation design is developed for survival responses. Assuming noninformative random censoring, asymptotic p values of relevant tests of equality of treatment effects are used to derive the assignment probability of incoming second stage subjects. Several ethical and inferential criteria of the design are studied, and are compared with those of an existing competitor. Applicability and performance of the proposed design are also illustrated using a data arising from a real clinical trial.