1. School of Economics and Management, Dalian Univ. of Technology, Dalian 116081, China; School of Statistics, Tianjin Univ. of Finance and Economics, Tianjin 300221, China.
2. Professor, School of Economics and Management, Dalian Univ. of Technology, Dalian 116081, China.
3. School of Economics and Management, Dalian Univ. of Technology, Dalian 116081, China (corresponding author).
4. School of Economics and Management, Dalian Univ. of Technology, Dalian 116081, China.