1. Heinz College and Department of Social and Decision Sciences, Carnegie Mellon University, 5000 Forbes Avenue, BP 319, Pittsburgh, PA 15213 (e-mail: )
2. International Food Policy Research Institute, Markets, Trade, and Institutions Division, 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: )
4. Tepper School of Business, Carnegie Mellon University, Pittsburgh, PA 15213 (e-mail: )