Common Problems in Impact Assessment Research

This contribution to the Impact Assessment Primer Series draws on selected case studies to describe common problems researchers confront in doing impact assessments of PSD programs, how researchers have dealt with these problems, and the related implications for the validity of the assessment findings. The frame of reference for discussing these issues is the minimally acceptable methodological standards established by the Private Sector Development Impact Assessment Initiative (PSD-IAI) in earlier Primer Series papers. The question this paper asks is whether the methodological approaches taken in the selected case studies satisfied minimally acceptable standards for a rigorous impact assessment.

The impact assessment problems discussed in this paper include: timing, spillover effects, selection bias, capability of local research partners, and unanticipated external factors, such as climatic disasters. These do not capture all the problems impact researchers face, but certainly the more common ones.