[1] Univ Ghent, Fac Med & Hlth Sci, Int Ctr Reprod Hlth ICRH, Dept Publ Hlth & Primary Care, C Heymanslaan 10 Entrance 75 ICRH, B-9000 Ghent, Belgium
[2] Tsinghua Univ, Res Ctr Med Sociol, Beijing, Peoples R China
[3] Wenzhou Med Univ, Sch Publ Hlth & Management, Wenzhou, Peoples R China
[4] Univ Ghent, Fac Med & Hlth Sci, Dept Internal Med & Paediat, Sect Geriatr, Ghent, Belgium
[5] Tsinghua Univ, Sch Social Sci, Dept Sociol, Beijing, Peoples R China
[6] Univ Libre Bruxelles ULB, Sch Publ Hlth, Brussels, Belgium