Bayesian adaptive cluster-randomized designs with long primary endpoints for pragmatic weight loss studies implemented in rural communities.

With the rise of obesity and other metabolic-related disorders since the early 2000s, there is a pressing need for innovative methods to reduce this trend. Many existing studies have long endpoints and protracted trial durations, often requiring substantial implementation costs. To address this, we propose the use of an adaptive trial design. This approach, which is at the forefront of research methodology, can significantly reduce the total duration of a trial, enhance participant outcomes by determining treatment efficacy earlier, and increase the number of participants randomized to the beneficial treatment groups. We suggest using a Bayesian Adaptive Cluster Randomized design to redesign the REPOWER trial, a weight loss study comparing behavioral interventions on weight loss in rural communities. Our approach incorporates an arm-dropping technique and will stop the trial early for futility if sufficient weight loss differences are not observed. We illustrate this by calculating operating characteristics under six scenarios to compare to the design used in the original trial.