[1] Kings Coll London, Florence Nightingale Fac Nursing Midwifery & Palli, Sch Nursing, London SE1 8WA, England
[2] Peking Univ, Beijing 100191, Peoples R China
[3] Hebei Med Univ, Sch Nursing, Shijiazhuang, Peoples R China
[4] Kunming Med Univ, Affiliated Hosp 1, Kunming, Peoples R China
[5] Northwest Womens & Childrens Hosp, Labour Room, Xian 710061, Peoples R China
[6] Peking Univ, Sch Nursing, Beijing 100191, Peoples R China