[1] Univ Groningen, Univ Med Ctr Groningen, Dept Gen Practice, NL-9700 AD Groningen, Netherlands
[2] Natl Inst Publ Hlth & Environm, Ctr Prevent & Hlth Serv Res, NL-3720 BA Bilthoven, Netherlands
[3] Municipal Publ Hlth Serv Groningen, Groningen, Netherlands
[4] Univ Groningen, Univ Med Ctr Groningen, Dept Internal Med, Rb Groningen, Netherlands