1. Guanghua School of Management, Peking University, Beijing 100871, People's Republic of China
2. School of Economics, Sichuan University, Chengdu 610065, People's Republic of China
3. Department of Statistics, Iowa State University, Ames, IA 50011, USA
4. Center for Statistical Science, Peking University, Beijing 100871, People's Republic of China
5. Department of Probability and Statistics, Peking University, Beijing 100871, People's Republic of China