[1] Shanghai Jiao Tong Univ, Sch Nursing, Shanghai 200025, Peoples R China
[2] Kings Coll London, Florence Nightingale Fac Nursing Midwifery & Palli, London SE1 8WA, England
[3] Jinyang Community Hlth Serv Ctr, Dept Childrens Dis Prevent, Shanghai 200136, Peoples R China
[4] Orebro Univ, Sch Med Sci, Clin Epidemiol & Biostat, S-70182 Orebro, Sweden
[5] Karolinska Inst, Inst Environm Med, Unit Integrat Epidemiol, S-17177 Stockholm, Sweden