Why do many international development evaluations have a positive bias? Should we worry?

Many of the approaches used by international development agencies to assess the impacts and effects of their development interventions can potentially result in the findings having a positive bias. As a consequence, impacts and benefits of the interventions are frequently overestimated, while the proportion of the target population who do not benefit may be underestimated and the potential negative consequences of the interventions may frequently be ignored. These biases are due to a combination of factors including: budget and time constraints; limited access to data—particularly baseline data; how evaluations are commissioned and managed; and political and organisational constraints and pressures. These biases have important consequences when evaluation findings are used to inform future management and policy decisions. While these biases are more obvious for under-resourced evaluations with unrealistically short deadlines, there are also a number of potential positive biases that can also affect well-resourced ‘strong’ quantitative evaluation designs. A number of recommendations are proposed to reduce positive bias and enhance the validity of evaluation findings by strengthening how evaluations are managed and increasing the rigour of the evaluation methodology, even when operating under budget and time constraints.