[1] Peking Univ, Sch Publ Hlth, Dept Hlth Policy & Management, 38 Xueyuan Rd, Beijing 100191, Peoples R China
[2] Harvard Med Sch, Boston Childrens Hosp, Dept Neurol, Boston, MA 02115 USA
[3] Harvard Med Sch, Boston Childrens Hosp, ICCTR Biostat & Res Design Ctr, Boston, MA 02115 USA
[4] Tilburg Univ, Dept Methodol & Stat, Tilburg, Netherlands