Background: Stepped wedge cluster randomized trials are a class of unidirectional crossover studies that have historically been limited to evaluating a single intervention. This design is especially suitable for pragmatic trials where the study feasibility can be improved with a phased introduction of the intervention. We examined variations of stepped wedge designs that would support evaluation of multiple interventions. Methods: We propose four different design variants for implementing a stepped wedge trial with two interventions: concurrent design, supplementation, replacement, and factorial designs. Analyses were conducted comparing the precision of the estimated intervention effects for the different designs. Results: Concurrent, supplementation, and factorial variants provide equal precision for estimating the treatment effect within a design for each of the interventions. However, in the replacement design, the effect of the first introduced intervention is generally estimated more precisely than the second intervention. Surprising and nonintuitive changes in the precision of the intervention effect estimates are observed when additional observation time intervals are included in multiple intervention designs. Conclusion: These stepped wedge design variations offer alternative methods for studying two interventions using a cluster-randomized trial. The selection of the appropriate variants should be driven by the research question with consideration given to the trade-off in number of steps, number of clusters, restrictions for concurrent implementation based on intervention characteristics, lingering effects of each intervention, and desired ability to compare interventions within clusters or within the same steps.
Lyons, Vivian H.; Li, Lingyu; Hughes, James; and Rowhani-Rahbar, Ali, "Evaluation of multiple interventions using a stepped wedge design" (June 2017). UW Biostatistics Working Paper Series. Working Paper 411.