1. Business School Central South University Changsha 410083 China
2. Institute of Metal Resources Strategy Central South University Changsha 410083 China
3. Department of Economics and Finance Southern Illinois University Edwardsville Edwardsville Illinois 62026‐1102 USA
4. Department of Accounting and Finance University of Otago Dunedin New Zealand
5. School of Mathematics and Statistics and Institute of Metal Resources Strategy Central South University Changsha 410083 China