Technical Note: Impact Evaluations
This note defines impact evaluations, explains when they should be commissioned according to USAID policy and describes different designs for quasi-experimental and experimental impact evaluations. The USAID Automated Directives System (ADS) 201 defines impact evaluations as those that measure the change in a development outcome that is attributable to a defined intervention. Impact evaluations are based on models of cause and effect and require a credible and rigorously defined counterfactual to control for factors other than the intervention that might account for the observed change.
This note outlines key considerations that USAID staff and evaluators should take into account when planning for and designing impact evaluations. Those commissioning an evaluation should include the evaluator when making decisions about an intervention’s targeting and implementation, and consider issues related to logistics, time, and cost. Therefore, although impact evaluations are a powerful tool to answer key questions about a particular intervention, they should be used selectively and only when appropriate in terms of purpose and funding.