1. School of Economics and Management, Shanghai Maritime University, Shanghai 201306, China
2. Center of Statistical Research, School of Statistics, Southwestern University of Finance and Economics, Chengdu 611130, Sichuan, China
3. School of Mathematics and Statistics, Northwestern Polytechnical University, Xi’an 710072, Shaanxi, China
4. School of Science, Xi’an Polytechnic University, Xi’an 710072, Shaanxi, China