Multiple actors and confounding factors: evaluating impact in complex social-ecological systems

The objective of impact evaluation is to establish causality between a programme, project or intervention and observed changes or effects, whether the changes are positive or negative, intended or unintended, and direct or indirect (OECD 2002). To accomplish this, impact evaluation must at a minimum undertake three tasks: fi rst, determine the extent of change that has taken place since the intervention started; second, establish a causal link between programme or project activities and the observed changes; and, third, discount or account for rival hypotheses or alternative feasible explanations that could account for the observed change.