[1] Univ Oslo, Dept Behav Sci Med, Inst Basic Med Sci, Fac Med, N-0317 Oslo, Norway
[2] Univ Oslo, Inst Gen Practice & Community Med, Fac Med, N-0317 Oslo, Norway
[3] Res Inst, Modum Bad, Norway
[4] Univ Tromso, Inst Community Med, N-9001 Tromso, Norway
[5] Univ Tromso, Fac Med, Inst Clin Med, N-9001 Tromso, Norway
[6] Univ Bergen, Dept Publ Hlth & Primary Hlth Care, N-5020 Bergen, Norway
[7] Univ Bergen, Dept Clin Med, Fac Med & Dent, N-5020 Bergen, Norway
[8] Norwegian Univ Sci & Technol, Dept Publ Hlth & Gen Practice, Dept Neurosci, Fac Med, N-7034 Trondheim, Norway
[9] Oslo Univ Coll, Fac Nursing, Oslo, Norway