1. School of Statistics and Mathematics, Guangdong University of Finance and Economics, Big data and Educational Statistics Application Laboratory, Guangzhou, PR China
2. School of Statistics and Mathematics, Guangdong University of Finance and Economics, Guangzhou, P. R. China
3. Department of Mathematics, Shanghai Jiao Tong University, Shanghai, P.R. China
4. Department of Mathematics, Sun Yat-sen University, Guangzhou, PR China