There used to be a touching belief that public health interventions were exempt from the kind of scrutiny that we might normally expect to be a pre-requisite for messing around with peoples’ bodies and their lives.¹ Even once it became accepted that physicians and surgeons could inadvertently do more harm than good, some areas of public health and health promotion occupied a privileged place. A few leaflets here, telling parents how to do their jobs better, a bit of social engineering there, trying to iron out a little local difficulty with housing or transport. What could be the harm in that? So long as people’s hearts were in the right place, brains were not thought to need to be quite so fully engaged in changing communities as in changing lipid lowering medication.

All that is now starting to change. The public health field of the Cochrane Collaboration is producing guidelines for those working in public health; the UK Medical Research Council² has produced guidelines on complex interventions, including those delivered at a population level for health promotion purposes, the Campbell Collaboration, which is a sister collaboration to Cochrane, but producing reviews in education, social welfare, and crime prevention is looking at the effectiveness of policies and practices ranging from boot camps for young offenders to mentoring.

Over the past few years, randomised controlled trials of day care,³ social support in pregnancy,⁴ sex education,⁵ and smoke alarms⁶ are among the studies conducted in non-clinical settings, with a public health purpose. Epidemiologists and social scientists working in tandem have ensured that as well as reporting health outcomes, issues of process and implementation are also considered. The qualitative methods …