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The last 10 years have seen an extraordinary surge of interest in ‘stepped wedge’ designs for evaluating interventions to improve health and social care. Reviews of published trials and registered protocols have shown an exponential increase in the number of trials citing a stepped wedge approach.1–6 A growing body of work on methods for the design, conduct and analysis of stepped wedge trials has emerged, building on seminal work by Hussey and Hughes in 2007.7 The Consolidated Standards of Reporting Trials reporting guidelines for stepped wedge cluster randomised trials are now available, making it easier for investigators to appraise evidence and plan their own evaluations.8
But published examples of stepped wedge evaluations in quality improvement illustrate some of the practical challenges. On the one hand, limited research resources may force investigators to stagger implementation at different sites9; on the other hand, persuading sites to follow a precise, predetermined schedule for implementation may be hard.10 In fact, investigators who plan a stepped wedge trial must balance a number of logistical, ethical and methodological issues.11 12 In this article, we focus predominantly on the design of such evaluations, and encourage a questioning approach. We take a ‘trial’ to mean a study involving the prospective, experimental allocation of interventions,13 but more particularly we focus on studies where those allocations are randomised. We start with the question of what is meant by a stepped wedge trial.
What is a stepped wedge cluster randomised trial?
The vast majority of stepped wedge trials are cluster randomised, and when people refer to stepped wedge designs this is usually what they have in mind. A cluster randomised trial is a trial in which all the participants at the same site or ‘cluster’ are allocated to the same intervention.14 Stepped wedge cluster randomised trials are run over an …
Funding RH is a Senior Fellow with The Healthcare Improvement Studies (THIS) Institute. This Fellowship is funded by a grant from the Health Foundation to the University of Cambridge.
Competing interests None declared.
Patient consent for publication Not required.
Provenance and peer review Commissioned; internally peer reviewed.