Evaluation of injury prevention interventions using the stepped wedge cluster randomised trial design: key considerations

Background Injury prevention interventions are often implemented at the group level via communities, hospitals, schools, etc, making cluster randomisation a suitable approach to evaluation. The stepped-wedge cluster randomised trial (SW-CRT) design has become increasingly popular for evaluating interventions in real-world settings. Method In this commentary, we describe the methodological characteristics of the SW-CRT design and highlight key threats to validity, relevant design and analytical issues, and scenarios in which the SW-CRT design might be a reasonable design choice. We illustrate these key points using a recently completed SW-CRT: the prehospital Canadian C-Spine trial. Results Seven potential biases associated with SW-CRTs, including: (1) secular trends, (2) confounding by external factors, (3) identification and recruitment bias, (4) contamination, (5) late and early transitioning, (6) risks of baseline imbalances due to small numbers of clusters and (7) statistical issues are discussed, along with potential mitigation strategies. Conclusion The SW-CRT design offers a pragmatic approach to evaluating injury prevention interventions that may involve a staggered rollout across services or regions. The design allows an intervention to be rolled out to all participating sites and provides an opportunity to efficiently evaluate effectiveness. It is important, however, for researchers to consider the unique design and analytic issues associated with the SW-CRT design. Mitigating potential threats to validity when using the SW-CRT design helps ensure robust evaluation of injury prevention interventions.