There are a number of reasons policy decisions are not more evidence-based but three predominate.
The first is simply that the research has not been conducted; for many important policy decisions it is impossible to be evidence-based because the evidence is currently not there.
Three other elements of the policy-making environment need to be borne in mind.
Policy-making is generally extremely fast by academic standards.
The first is the relatively limited range of things policymakers can do.
They can exhort; in some cases they can legislate; most commonly they deploy resources but this means moving resources from one priority to another rather than creating new resource.Barriers include the evidence not being there; lack of demand by policymakers; academics not producing rigorous, relevant papers within the timeframe of the policy cycle. Academics underestimate the speed of the policy process, and publish excellent papers after a policy decision rather than good ones before it.To be useful in policy, papers must be at least as rigorous about reporting their methods as for other academic uses.The second follows from the fact that their main lever is moving constrained resources around and choosing between different ratios of financial allocation; they tend to think like economists or be advised by them, and economics is the training for many policymakers, whether civil servants or politicians.This does not mean good economic analysis is essential to influence policy (although it certainly helps), but good policymakers will always be asking the question ‘what is the opportunity cost of this new initiative? Policymakers also therefore can be more numerate than scientists often give them credit for, and have access to well trained statisticians.Policy decisions are invariably weakened when they do not take account of the best current knowledge.Incorporating relevant research findings into policy and practice should therefore be central to the aims of those undertaking practically oriented health research, including in the basic and social sciences.Papers which are as simple as possible (but no simpler) are most likely to be taken up in policy.Most policy questions have many scientific questions, from different disciplines, within them.What makes a good scientific policy paper, defined as a paper likely to influence and improve policy decisions based on science?The starting point for any piece of communication, and a scientific paper is a form of communication, is: who is the audience?