1. Professor, College of Management and Economics, Tianjin Univ., Tianjin 300072, PR China.
2. Postgraduate Student, College of Management and Economics, Tianjin Univ., Tianjin 300072, PR China (corresponding author).
3. Postgraduate Student, College of Management and Economics, Tianjin Univ., Tianjin 300072, PR China.
4. Undergraduate Student, College of Management and Economics, Tianjin Univ., Tianjin 300072, PR China.