1. Department of Management, London School of Economics and Political Science, Houghton Street, London WC2A 2AE (e-mail: )
2. Graduate School of Business, Columbia University, 3022 Broadway, Uris Hall 625 New York, NY 10027 (e-mail: )
3. Kellogg School of Management, Northwestern University, 2001 Sheridan Road, Evanston, IL 60201 (e-mail: )