In this article, a group sequential test (GST) of non-parametric statistics for survival data is briefly reviewed. An asymptotic joint distribution of the test statistics, obtained after each interim analysis, is given to illustrate the applicability of the critical values of the GST procedures. It should be noted that censored observations are generally seen in survival data. Therefore, if one makes power calculations irrespective of censoring, reliable results may not be achieved, due to the lack of information about the censoring structure. A wide simulation study, covering different censoring rates and tied observations, is conducted to make the power comparisons under various scenarios. The simulation results are interpreted and compared with the results obtained by using power analysis and sample size (PASS) software.
Group sequential designs are widely used in Phase II clinical trials, which are usually undertaken to evaluate the response probability of specific treatment regimen. In most randomized clinical trials with sequential patient entry, fixed sample size design is unjustified on ethical grounds and sequential designs are often impractical. However group sequential designs are generally more practical and they provide much of the saving possible from sequential designs. Optimal restricted two-stage design is the simplest form of a group sequential design. In this study, group sequential design obtained by () t * α functions characterized using the type-I error probability and optimal restricted two stage design has been compared for the cases that the group sizes are equal. Furthermore, their efficiency regarding fixed sample size design has been calculated and the results have been discussed.
In clinical trials, it is important to set up a design to reach a decision on effectiveness of a drug in treating a disease with the loss of the minimum number of patients. Group sequential designs are very beneficial on this point. However, the proportional hazards assumption must hold to work under a group sequential design properly. A trial running under a group sequential design covers a long time period; therefore, assuming that hazards remain proportional over a long time period is somewhat unrealistic. We should examine and figure out the impact of nonproportional hazards over the hypothesis tests conducted under a group sequential design to set up more reliable designs and decide which test to use in which conditions. In this article, powers of group sequential tests with nonparametric statistics are evaluated under nonproportional hazards by a Monte Carlo simulation study. The simulation study covers different nonproportional hazards scenarios, censoring rates, survival distributions, sample sizes, and tied observations. With this study, we intend to be helpful for clinical trial designers to set up a more reliable group sequential design.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.