[1] Univ Oslo, Oslo, Norway
[2] Oslo Univ Hosp, Oslo, Norway
[3] Univ Tromso, Tromso, Norway
[4] McMaster Univ, 1280 Main St West,Room HSC-2C12, Hamilton, ON L8N 3Z5, Canada
[5] Univ Oslo, Clin Effectiveness Res Grp, POB 1089 Blindern, N-0318 Oslo, Norway
[6] Univ Oslo, Clin Effectiveness Res Grp, Sognsvannsveien 21, N-0372 Oslo, Norway
[7] Univ Oslo, Inst Hlth & Soc, POB 1089 Blindern, N-0318 Oslo, Norway
[8] Univ Oslo, Clin Effectiveness Grp, Fac Med, Problemveien 7, N-0315 Oslo, Norway