1. School of Advanced Agricultural Sciences, Peking University, No. 5 Yiheyuan Road, Haidian District, Beijing 100871, China
2. Center for Chinese Agricultural Policy, Institute of Geographical Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing, China
3. Department of Economics, University of Lethbridge, Lethbridge, Alberta T1K 3M4, Canada
4. Center for Regulation and Market Analysis, School of Commerce, University of South Australia Business School, Adelaide, South Australia, Australia