Two concepts of evidence-based policy

Abstract

The notion that public policies should be evidence-based has gained increasing 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 ground policy decisions in evidence: evidence as a restriction, which operates as a necessary condition for the admissibility of alternatives; and evidence as a preference criteria, 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 can hardly be combined simultaneously without generating practical contradictions. The key contributions provide a normative typology that facilitates the diagnosis of tensions in evidence use, positions this distinction in relation to classical typologies in the literature, and guides the institutional design of scientific advisory systems in democratic contexts.