1. Department of Economics, MIT, The Morris and Sophie Chang Building, 50 Memorial Drive, E52-550, Cambridge, MA 02142 (email: )
2. Columbia Business School, Uris Hall 606, 3022 Broadway, New York, NY 10027 (email: )
3. University of Illinois at Urbana-Champaign, 109 David Kinley Hall, 1407 W. Gregory, Urbana, IL 61801 (email: )