Two concepts of evidence-based policy

The notion that public policy should be evidence-based has gained prominence in recent years, attracting both supporters and critics. This article argues that a significant part of this debate stems from the coexistence of two distinct conceptions of what it means to base policy decisions on evidence: evidence as a restriction, which operates as a necessary condition for the admissibility of options; and evidence as a preference criterion, which guides the selection among options already legitimized by political or normative criteria. The article defines these two concepts, analyzes their respective advantages and limitations, and demonstrates that, under plausible assumptions, each approach can be applied in isolation, but hardly simultaneously without practical contradictions. The key contributions offer a normative typology that allows for diagnosing tensions in the use of evidence, positions this distinction in relation to classical typologies in the literature, and guides the institutional design of scientific advisory systems in democratic contexts.

Keywords:
evidence-based policy; evidence-informed policy; decision theory; public choice theory; policy evaluation