1. College of Economics, Sichuan Agriculture University, Chengdu, China
2. School of Economics and Management, Huazhong Agriculture University, Wuhan, China
3. School of Economics and Management, Southwest Jiaotong University, Chengdu, China
4. Yibin Research Institute, Southwest Jiaotong University, Yibin, China
5. Department of Economics, Ohio University, Athens, Ohio, USA