Correspondence to: Fang Wang, West China School of Nursing, Sichuan University / Innovation Center of Nursing Research, Nursing Key Laboratory of Sichuan Province, West China Hospital, Sichuan University, Chengdu, Sichuan P. R, 610041, China. E-mail:
bio_wangf@163.com Guan Wang, West China School of Nursing, Sichuan University / Innovation Center of Nursing Research, Nursing Key Laboratory of Sichuan Province, West China Hospital, Sichuan University, Chengdu, Sichuan P. R, 610041, China. E-mail:
guan8079@163.com