In an ideal world new policies and interventions could be tested in a randomised fashion before implementation. But, all to often, policies within the health service are decided upon in the absence of decent evidence to serve political rather than public health or economic ends. Consider the recent case of the 7-day NHS, which the evidence is beginning to show will likely not produce the benefits expected of it. Researchers cannot expect political decisions to be delayed for them to be able to conduct the ideal study. Sometimes the researcher has to evaluate a policy or organisation change that will go ahead regardless or one that cannot be reversed once it is in place. Nevertheless, this can still produce a good opportunity for evaluation that can satisfy both researchers and policy makers alike: the stepped wedge cluster randomised trial.
The stepped wedge trial design is a variant on the cluster RCT design. The Figure below illustrates the different set-ups. What is unique to the stepped wedge design is that by the end of the study all of the study sites will receive the intervention: it is the order in which they receive the intervention that is randomised. Hemming et al (2015) provide a good overview with examples of the stepped wedge trial, while Hemming, Girling, and Lilford (2015) give a statistical rationale and background. And, recently Girling and Hemming (2016) have investigated hybrid designs to optimize statistical efficiency.
Figure. Schematic illustration of the conventional parallel cluster study (with variations) and the stepped wedge study. Hemming et al. (CC BY 4.0)
The stepped wedge design presents an attractive proposition and compromise for researchers and policy makers alike. But the feasibility of implementing it depends on the stage when the researchers are involved in the design of the roll out of the intervention. Often it is the case that researchers are involved after the fact, opportunistically examining an ongoing change in the health system. However, there are a growing number of examples of stepped wedge studies being implemented in the NHS (e.g. here). Researcher involvement with policy and organisational changes in the health system should become an opt-out system rather than opt-in. Data is readily available and the intervention will already be planned making such research relatively cheap. The NHS can become a powerful policy laboratory.
Photo credit: As6022014 (CC BY-SA 3.0)
