[1] Witten Herdecke Univ, Fac Hlth, Inst Gen Practice & Family Med, Alfred Herrhausen Str 50, D-58448 Witten, Germany
[2] Maastricht Univ, Fac Hlth Med & Lifesci, Dept Hlth Eth & Soc, Debyepl 1, NL-6229 HA Maastricht, Netherlands
[3] Univ Manchester, Sch Hlth Sci, Div Populat Hlth Hlth Serv Res & Primary Care, Oxford Rd 176, Manchester M13 9PL, Lancs, England