1. Innovation Center of Nursing Research Nursing Key Laboratory of Sichuan Province West China Hospital, and West China School of Nursing Sichuan University Chengdu 610041 China
2. School of Management Fudan University Shanghai 200433 China
3. Department of Mathematics National University of Singapore Kent Ridge Road Singapore 119077 Singapore
4. School of Economics Sichuan University Chengdu 610045 China
5. School of Mathematics and Information China West Normal University Sichuan 637002 China