1. School of Statistics, Qufu Normal University, Qufu, Shandong 273165, China
2. School of Insurance, Shandong University of Finance and Economics, Jinan, Shandong 250014, China
3. School of Statistics and Information, Shanghai University of International Business and Economics, Shanghai 201620, China
4. School of Statistics, Shandong University of Finance and Economics, Jinan, Shandong 250014, China