What Is Evidence-Based Policymaking?

#The core idea

The phrase is borrowed from evidence-based medicine, articulated in the 1990s by David Sackett and colleagues as “the conscientious, explicit and judicious use of current best evidence” in clinical decisions. Applied to policy, the same discipline asks of any proposed programme: what is the best evidence that it achieves its aims, how strong is that evidence, and what would it take to find out?

The practical shift it demands is subtle but real: from asking whether a study exists that supports a position, to asking how strong the overall body of evidence is — including the studies that point the other way.

#What counts as evidence

Research designs differ in how well they can support causal claims. Randomised controlled trials and strong natural experiments can isolate a programme’s effect; observational studies can establish associations and generate hypotheses; qualitative work explains mechanisms and context. So-called evidence hierarchies rank designs by their resistance to bias — a useful shorthand, provided it is read as a statement about causal questions specifically, not about the worth of research in general.

Modern practice grades bodies of evidence rather than single studies. Frameworks such as GRADE, developed for health guidelines and widely adapted since, rate the certainty of evidence (high to very low) by considering study design, consistency, precision and risk of bias together. Systematic reviews and meta-analyses are the workhorses: they gather all studies meeting pre-stated criteria, appraise them, and synthesise the result.

#The institutions built around it

• What Works centres (United Kingdom). Since 2013 the What Works Network has funded centres that commission and translate evidence for specific fields — education, policing, early intervention, local growth — into ratings and toolkits for practitioners.
• The Foundations for Evidence-Based Policymaking Act (United States, 2018). Requires federal agencies to publish evidence-building plans, appoint evaluation officers, and improve researcher access to government data.
• Systematic-review organisations. The Campbell Collaboration produces systematic reviews in social policy, education and crime, applying the model its sibling, Cochrane, established for health care.
• Evaluation and audit bodies. National audit offices, budget offices and dedicated evaluation units increasingly assess not only whether money was spent lawfully but whether programmes achieved measurable results.

#What it looks like in practice

In day-to-day government, evidence-based practice usually means: piloting programmes before national roll-out; building evaluation into programme design rather than bolting it on afterwards; pre-stating success measures; publishing results whether or not they flatter the programme; and sunsetting interventions that repeated evaluation finds ineffective. Mexico’s PROGRESA conditional cash-transfer programme, launched in 1997 with a randomised roll-out, remains the canonical example: its published evaluations shaped social policy across many countries.

#Honest limits

• Evidence cannot settle values. Studies can estimate a policy’s effects; they cannot decide how much weight a society should give to competing goals. “What works” always implies “works for a stated objective”.
• External validity is never free. Effects measured in one country, era or population need not transfer. The disciplined response is replication and local piloting, not assumption.
• Timescales collide. Political decisions are often required in months; rigorous evaluation takes years. Interim decisions must be made under uncertainty — the evidence-based habit is to say so explicitly.
• Evidence can be selectively deployed. Cherry-picking congenial studies is the failure mode the whole apparatus of systematic review exists to prevent.

#Sources and further reading

• Sackett et al. (1996), “Evidence based medicine: what it is and what it isn’t”, BMJ — the founding statement of the evidence-based approach.
• UK What Works Network — official documentation of the centres and their evidence standards.
• Campbell Collaboration — systematic reviews of social and policy interventions.
• Foundations for Evidence-Based Policymaking Act of 2018 — the US statutory framework for federal evidence-building.