[1] Univ North Carolina Chapel Hill, Dept Hlth Policy & Management, Gillings Sch Global Publ Hlth, Chapel Hill, NC USA
[2] Sichuan Univ, West China Sch Publ Hlth, Chengdu, Peoples R China
[3] Stanford Univ, Stanford Ctr Chinas Econ & Inst, Stanford, CA 94305 USA
[4] Univ North Carolina Chapel Hill, Dept Maternal & Child Hlth, Gillings Sch Global Publ Hlth, Chapel Hill, NC USA
[5] Univ Nevada, Sch Publ Hlth, Dept Biostat Epidemiol & Environm Hlth, Reno, NV 89557 USA
[6] Stanford Univ, Dept Pediat, Sch Med, Stanford, CA 94305 USA