Evidence-based policy: where is our theory of evidence?

This article critically analyses the concept of evidence in evidence-based policy, arguing that there is a key problem: there is no existing practicable theory of evidence, one which is philosophically-grounded and yet applicable for evidence-based policy. The article critically considers both philosophical accounts of evidence and practical treatments of evidence in evidence-based policy. It argues that both fail in different ways to provide a theory of evidence that is adequate for evidence-based policy. The article contributes to the debate about how evidence can and should be used to reduce contingency in science and in policy based on science.