Methodological challenges of evaluating the impact of the Global Environment Facility's biodiversity program

In this paper, we explore some of the methodological challenges that evaluators face in assessing the impacts of complex intervention strategies. We illustrate these challenges, using the specific example of an impact evaluation of one of the six focal areas of the Global Environment Facility; its biodiversity program. The discussion is structured around the concepts of attribution and aggregation, offering the reader a framework for reflection. Subsequently, the paper discusses how theory-based evaluation can provide a basis for addressing the attribution and aggregation challenges presented.