1. Institute for International Economic Studies, Stockholm University, SE-106 91 Stockholm, Sweden.
2. Department of Economics, National Taiwan University, 21 Hsu-Chow Road, Taipei 100, Taiwan.
3. Management and Organization, Kellogg School of Management, Northwestern University, Evanston, IL 60201.
4. Division for the Humanities and Social Sciences, MC 228-77, California Institute of Technology, Pasadena, CA 91125.