1. Department of Population, Family, and Reproductive Health, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD 21205, USA
2. Johns Hopkins School of Nursing, 525N Wolfe Street, Baltimore, MD 21205, USA
3. Xin Hua Hospital, School of Medicine, Shanghai Jiao Tong University, Shanghai 200240, China
4. School of Nursing, Shanghai Jiao Tong University, Shanghai 200240, China