The findings, interpretations, and conclusions expressed in this paper are entirely those of the authors. They do not necessarily represent the views of the World Bank, its Executive Directors, or the countries they represent. The paper should not be cited without the permission of the authors. We are grateful to Tyler Biggs of the Africa Technical Department of the World Bank for making available the data upon which this paper is based. We received helpful comments from participants at a symposium at the Eindhoven Technical University. A. Szirmai provided many helpful suggestions.