1. Olin School of Business, Washington University in St. Louis, One Brookings Drive, St. Louis, MO 63130 (e-mail: )
2. Department of Economics, Duke University, 419 Chapel Drive, Durham, NC 27708 (e-mail: )
3. Department of Economics, London School of Economics and Political Science, Houghton Street, London WC2A 2AE, UK (e-mail: )
4. Division of Humanities and Social Sciences, California Institute of Technology, 1200 E. California Blvd., Pasadena CA 91125 (e-mail: )