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Pragmatic Clinical Trials Unit

Stepped Wedge Trials

In 1948 the UK Medical Research Council’s streptomycin trial established the principles of the modern randomised controlled trial, which revolutionised health research. The parallel groups design used in that first trial has proved to be remarkably enduring, but variations and innovations in trial design continue to be explored. Innovation may be needed to tackle practical constraints on trial conduct, but it can also help us improve the efficiency of a trial – that is to reduce the number of participants or other resources needed to gather the evidence we need.

Stepped wedge trials are cluster randomised trials in which the clusters are sampled repeatedly over time, with different clusters crossing over from the control to the experimental intervention at different times. They can have practical advantages over parallel group trials, but they can also be more efficient in some circumstances. A much fuller understanding has emerged over the last few years of theoretically optimal schemes for stepped wedge designs, but there are still many challenges in the implementation, analysis and reporting of stepped wedge trials that we are keen to investigate.

The following are useful, introductory articles on stepped wedge trials:

Hooper R, Eldridge SM. Cutting edge or blunt instrument: how to decide if a stepped wedge design is right for you. Bmj Quality & Safety 2021;30:245-250

Hooper R. Key concepts in clinical epidemiology: Stepped wedge trials. Journal of Clinical Epidemiology 2021;137:159-162

Some of our recent research is also summarised here:

Hooper R. Designing stepped wedge trials with continuous recruitment. NIH Methods: Mind the Gap webinar series.

For more background and resources on stepped wedge trials you can also visit the Stepped Wedgehog website.


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