Institute of Statistics and Applied Mathematics Anhui University of Finance and Economics Bengbu 233030 China;
Department of Statistics and Finance University of Science and Technology of China Hefei 230022 China;
Institute of Statistics and Applied Mathematics Anhui University of Finance and Economics Bengbu 233030 China;
Department of Statistics and Finance University of Science and Technology of China Hefei 230022 China;
Department of Statistics and Finance University of Science and Technology of China Hefei 230022 China;