1. Booth School of Business, University of Chicago, 5807 S. Woodlawn Avenue, Chicago, IL 60637 (e-mail: )
2. Department of Economics, Harvard University, 1805 Cambridge Street, Cambridge, MA 02138 (e-mail: )
3. Department of Economics, University of California-Los Angeles, 8283 Bunche Hall, Los Angeles, CA 90095 (e-mail: )
4. Tepper School of Business, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, PA 15213 (e-mail: )