Empirical validity of the evaluation of public policies: models of evaluation and quality of evidence

There is a wide range of evaluation methods. On the basis of which criteria should one methodbe chosen? On what scientific foundations are the results of numerous evaluations based? Howcan reliability and empirical validity be tested? The relevance of such questions is heightened innew fields of action such as agri-environmental policy. This paper aims to demonstrate thattheoretical advances on level and types of evidence (existence, causality, effectiveness) can helpresolve these issues. The main evaluation methods are classified into three main categories,according to their main goal (to learn, measure, understand) and linked to the debate on typesof evidence. The analysis is illustrated by comparing evaluation methods in the field of agroenvironmentalpolicies and farm advisory services. Attention is drawn to the shortcomings ofeach method with respect to corroborating facts as well as existing complementarities andtrade-offs between methods in terms of empirical validity.