1. Heinz College and Department of Social and Decision Sciences, Carnegie Mellon University, 5000 Forbes Avenue, BP 319B, Pittsburgh, PA 15213 (e-mail: )
2. Markets, Trade, and Institutions Division, International Food Policy Research Institute, 2033 K Street NW, Washington, DC 20006 (e-mail: )
3. Department of Economics, University of Pittsburgh, 4928 WW Posvar Hall, Pittsburgh, PA 15260 and NBER (e-mail: )