What Constitutes "Good" Evidence for Public Health and Social Policy-making? From Hierarchies to Appropriateness

Within public health, and increasingly other areas of social policy, there are widespread calls to increase or improve the use of evidence for policy-making. Often these calls rest on an assumption that increased evidence utilisation will be a more efficient or effective means of achieving social goals. Yet a clear elucidation of what can be considered "good evidence" for policy is rarely articulated. Many of the current discussions of best practise in the health policy sector derive from the evidence-based medicine (EBM) movement, embracing the "hierarchy of evidence" that places experimental trials as pre-eminent in terms of methodological quality. However, a number of problems arise if these hierarchies are used to rank or prioritise policy relevance. Challenges in applying evidence hierarchies to policy questions arise from the fact that the EBM hierarchies rank evidence of intervention effect on a specified and limited number of outcomes. Previous authors have noted that evidence forms at the top of such hierarchies typically serve the needs and realities of clinical medicine, but not necessarily public policy. We build on past insights by applying three disciplinary perspectives from political science, the philosophy of science and the sociology of knowledge to illustrate the limitations of a single evidence hierarchy to guide health policy choices, while simultaneously providing new conceptualisations suited to achieve health sector goals. In doing so, we provide an alternative approach that re-frames "good" evidence for health policy as a question of appropriateness. Rather than adhering to a single hierarchy of evidence to judge what constitutes "good" evidence for policy, it is more useful to examine evidence through the lens of appropriateness. The form of evidence, the determination of relevant categories and variables, and the weight given to any piece of evidence, must suit the policy needs at hand. A more robust and critical examination of relevant and appropriate evidence can ensure that the best possible evidence of various forms is used to achieve health policy goals.