A Contribution to Current Debates in Impact Evaluation

A debate on approaches to impact evaluation has raged in development circles in recent years. This paper makes a contribution to this debate through discussion of four issues. First, I point out that there are two definitions of impact evaluation. Neither is right or wrong, but they refer to completely different things. There is no point in methodological debates unless they agree a common starting point. Second, I argue that there is confusion between counterfactuals, which are implied by the definition of impact evaluation adopted in this paper, and control groups, which are not always necessary to construct a counterfactual. Third, I address contribution rather than attribution — a distinction that is also definitional, mistaking claims of attribution to mean sole attribution. I then consider accusations of being ‘positivist’ and ‘linear’, which are, respectively, correct and unclear. Finally, I suggest that these arguments do not mean that there is a hierarchy of methods, rather quantitative approaches, including RCTs, are often the most appropriate methods for evaluating the impact of a large range of interventions, having the added advantage of allowing analysis of cost effectiveness or cost-benefit analysis.