1. Department of Social and Decision Sciences, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, PA 15213, and NBER (e-mail: )
2. Graduate School of Economics and Business Administration, Hokkaido University, Kita 9, Nishi 7, Kitaku, Sapporo 060-0809, Japan (e-mail: )
3. Faculty of Economics, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan (e-mail: )
4. Booth School of Business, University of Chicago, 5807 S. Woodlawn Avenue, Chicago, IL 60637, and NBER (e-mail: )