[1] Univ Med Ctr Rotterdam, Erasmus MC, Dept Gen Practice, POB 2040, NL-3000 CA Rotterdam, Netherlands
[2] Northwestern Univ, Feinberg Sch Med, Dept Social Med Sci, 625 N Michigan Ave,27th Floor, Chicago, IL 60611 USA
[3] North Shore Univ Hlth Syst, Dept Family Med, Res Inst, 1001 Univ Pl, Evanston, IL 60201 USA
[4] Univ Leuven, KU Leuven, Inst Healthcare Policy LIGB, Kapucijnenvoer 35,Blok D Bus 7001, B-3000 Louvain, Belgium
[5] Netherlands Inst Hlth Serv Res NIVEL, POB 1568, NL-3500 BN Utrecht, Netherlands
[6] Radboud Univ Nijmegen, Dept Sociol, POB 9104, NL-6500 HE Nijmegen, Netherlands