Relationship between evidence and policy: A case of evidence-based policy or policy-based evidence?

The evidence base in public health is claimed to be weak, lacking the rigour of, for example, clinical care. But perhaps the problem lies not so much in poor evidence but the methods used to assemble it and the political context in which that evidence then gets drawn upon (or not) to inform policy. Public health interventions often demand a process of social change and their effectiveness is the result of a complex mix of influences: leadership, changing environments, organisational history and culture, and so on. In such complex systems the type of evidence that can best inform policy is not reducible to clinical trials or experimental designs of the type that dominate evidence-based medicine. In studying complex, unstable and nonlinear social change sought by many public health interventions aimed at improving health and tackling health inequalities, acquiring evidence on how something works and in what contexts becomes critical. Failure to use research might be because it is seen as threatening to existing power relationships rather than because the evidence is insufficiently robust. Research is only likely to be useful in influencing and shaping policy if researchers and policy-makers engage with each other from the inception of the research to its completion. This lecture will review the implications of such an approach and argues that its strength is that it is sensitive to different contexts and therefore may have appeal at a global level especially in informing public health policy in countries with very different priorities, resources and levels of development.