The Politics of Evidence: Why Good Research Alone Is Never Enough
Evidence Doesn't Speak for Itself.
The term “evidence-based policymaking” (EBPM) has acquired a quality that Paul Cairney (2017) describes as “valence”. It is so intuitively appealing that it becomes almost impossible to oppose. Who, after all, would argue for policies made in the absence of evidence? Yet precisely because the term feels altruistic, its implications are rarely examined with care. Once subjected to scrutiny, the concept proves considerably more fragile than it seems.
The analogy most commonly invoked is evidence-based medicine (EBM), a framework built on a relatively stable hierarchy of methodological rigour, with randomised control trials (RCTs) at the apex, followed by systematic reviews, cohort studies, and so on, in which the expectation is that practitioners align their decisions with the best available evidence (Oliver et al., 2014a; 2014b). The logic is coherent within its domain: a controlled clinical setting, a defined intervention, a measurable outcome. Policymaking shares none of these features. There is no agreed hierarchy of evidence, no controlled setting, and no single authoritative decision-maker. What policymaking has, instead, is politics.
Bounded Rationality and the Limits of the Rational Ideal
The theoretical starting point for any serious analysis of EBPM is Herbert Simon’s (1976) concept of bounded rationality. Policymakers operate under conditions of cognitive and informational constraint: time is limited and problems are complex. The amount of potentially relevant evidence far exceeds any individual’s or institution’s capacity to process it. In response, decision-makers rely on heuristics, cognitive shortcuts that simplify judgement. Some of these shortcuts are deliberate and goal-directed: deferring to trusted advisors, privileging familiar information sources, filtering evidence through established institutional frameworks. Others are less conscious, relying on gut instinct and personal bias (Cairney, 2017).
The critical implication of bounded rationality is that evidence never enters a neutral space. It enters a mind that is already engaged in sorting, filtering, and prioritising. As Cairney (2017) notes, most contemporary policy theories treat bounded rationality not as something to fix, but as the fundamental condition of governing. To speak of “evidence-based” policy is, in this view, to describe an ideal type that bears little resemblance to the actual mechanics of decision-making.
Comprehensive rationality, the ideal in which decision-makers survey all available options, weigh all consequences, and select the optimal course of action, has long been treated in the policy literature as a normative benchmark against which real-world behaviour falls short. The EBPM agenda can be read as the latest iteration of this ambition: a renewed effort to bring systematic knowledge to bear on public decisions. What the bounded rationality literature suggests, however, is that this ambition consistently founders not due to a lack of good evidence, but on the structural features of the environments in which policymaking takes place.
What Evidence Must do to Gain Traction
Bounded rationality does not disappear once evidence enters the policy process, it shapes the conditions under which evidence can gain traction at all. Cairney (2017) identifies a set of overlapping strategies that actors must employ to move evidence toward influence. Attention must first be secured. Baumgartner et al. (2018) shows that policy change more often follows shifts in how issues are framed than from the emergence of new evidence, meaning factual claims must be paired with emotional appeals to prompt movement in policymaker attention. Evidence must also be narrativised. Shanahan et al. (2018) demonstrates that simple, morally legible stories that assign clear causes and apportion blame consistently outcompete technically sophisticated arguments in the contest for political salience.
Beyond framing, evidence must contend with the belief structures of dominant coalitions (Weible et al., 2012). And even where framing and coalition alignment are achieved, timing remains a constraint largely independent of the evidence’s quality. Kingdon (1984) argues that policy windows open rarely and close quickly, such that evidence not positioned within the right network at the right moment is likely to be passed over regardless of its quality.
Evidence Is Inevitably Political
A tempting response to the foregoing analysis is to treat framing, networks, and timing as obstacles to be overcome. Barriers between science and policy that better institutional design might dissolve. This framing, however, misunderstands the nature of policymaking. These factors are core features of any system in which public decisions must be negotiated across the complex landscape of democracy. Even in governments with strong analytical traditions and high state capacity, evidence must compete with other legitimate considerations such as public preferences and coalition constraints. A policymaking process that simply implemented the findings of the best available research would potentially bypass other democratic processes. The goal then, is not to insulate policy from politics, but to ensure that evidence has a genuine and consequential role within the political process. That it survives the filters, rather than being eliminated by them.