The suitability of cluster randomised trials for evaluating interventions directed at whole communities or organisations remains vexed.1
It need not be.2
Some health promotion advocates (including the WHO European working group on health promotion evaluation) believe randomised controlled trials are inappropriate because of the perceived requirement for interventions in different sites to be standardised or look the same.1,3,4
They have abandoned randomised trials because they think context level adaptation, which is essential for interventions to work, is precluded by trial designs. An example of context level adaptation might be adjusting educational materials to suit various local learning styles and literacy levels.
Lead thinkers in complex interventions, such as the UK's Medical Research Council, also think that trials of complex interventions must “consistently provide as close to the same intervention as possible” by “standardising the content and delivery of the intervention.”5
By contrast, however, they do not see this as a reason to reject randomised controlled trials.
These divergent views have led to problems on two fronts. Firstly, the field of health promotion is being turned away from randomised controlled trials.1,3,4
This could have heavy consequences for the future accumulation of high quality evidence about prevention. Secondly, when trials with organisations and whole communities do go ahead, the story is consistently becoming one of expensive failure—that is, weak or non-significant findings at huge cost.6-8
Could one of the reasons for the interventions not working be that the components have been overly standardised?
Something has to change. The current view about standardisation is at odds with the notion of complex systems. We believe that an alternative way to view standardisation could allow state of the art interventions (and ones that might look different in different sites) to be more effective and to be meaningfully evaluated in a randomised controlled trial. First, however, we have to re-examine our understanding of the term complex intervention.