1. School of Economics, Lanzhou University, Lanzhou, China
2. School of Statistics, Lanzhou University of Finance and Economics, Lanzhou, China
3. Faculty of Economics, Administrative and Social Sciences, Nisantasi University, Istanbul, Turkey;
4. Department of Medical Research, China Medical University Hospital, China Medical University, Taichung, Taiwan
5. Canadore College, Canadore at Stanford, North Bay, Canada
6. College of Economics, Sichuan Agricultural University, Chengdu, China