Qimin Zhan1, Shaomei Shang2, Wenkai Li3, Lincoln Chen4. 1. Peking University Health Science Centre, Beijing 100191, China. Electronic address: qiminzhan@vip.163.com. 2. Peking University, School of Nursing, Beijing 100191, China. 3. China Medical Board, Beijing Office, Beijing, China. 4. China Medical Board, Cambridge, MA, USA.