1. School of Economics and Management and National Institute for Fiscal Studies, Tsinghua University, Beijing, China 100084 (email: )
2. Division of Social Science, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong (email: )
3. Institute of Social and Economic Research, Osaka University, 6-1 Mihogaoka, Ibaraki, Osaka 567-0047, Japan (email: )