1. PhD candidate, Department of Agricultural and Resource Economics, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan.
2. Associate Professor, Department of Agricultural and Resource Economics, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan.
3. Professor, College of Economics and Management, China Agricultural University, No.17 Tsinghua East Road, Haidian District, Beijing 100083, China P.R.
4. Professor, Department of Agricultural and Resource Economics, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan.