In this issue, various authors hope to clarify and elucidate what impact evaluations are and when they are effective tools for learning: we believe they have become an indispensable tool for measuring and improving the impact of projects and policies on decreasing poverty and – what is equally important – setting precise and realistic aspirations for the future.

What is an impact evaluation?

For many years, the development community – including the Development Assistance Committee of the Organisation for Economic Co-operation and Development (OECD-DAC) in its Criteria for Evaluating Development Assistance – used the term “impact” to refer to the final level of the causal theory of change, or log frame. This definition has been replaced in recent years, and impact evaluations are now seen as “an objective assessment of the change that can be directly attributed to a project, programme or policy”. This could be the impact of an information campaign (about the importance of crop rotation) on farmer output, or it could be the effect of introducing rainfall insurance on a farmer’s choice of crops.