Designing and conducting adaptive trials to evaluate interventions in health services and implementation research: practical considerations

Randomised controlled clinical trials are widely considered the preferred method for evaluating the efficacy or effectiveness of interventions in healthcare. Adaptive trials incorporate changes as the study proceeds, such as modifying allocation probabilities or eliminating treatment arms that are likely to be ineffective. These designs have been widely used in drug discovery studies but can also be useful in health services and implementation research and have been minimally used. In this article, we use an ongoing adaptive trial and two completed parallel group studies as motivating examples to highlight the potential advantages, disadvantages, and important considerations when using adaptive trial designs in health services and implementation research. We also investigate the impact on power and the study duration if the two completed parallel group trials had instead been conducted using adaptive principles. Compared with traditional trial designs, adaptive designs can often allow the evaluation of more interventions, adjust participant allocation probabilities (eg, to achieve covariate balance), and identify participants who are likely to agree to enrol. These features could reduce resources needed to conduct a trial. However, adaptive trials have potential disadvantages and practical aspects that need to be considered, most notably: outcomes that can be rapidly measured and extracted (eg, long term outcomes that take considerable time to measure from data sources can be challenging), minimal missing data, and time trends. In conclusion, adaptive designs are a promising approach to help identify how best to implement evidence based interventions into real world practice in health services and implementation research.