[1] Univ Oslo, Natl Hosp, Stavern, Hosp Rehabil,Dept Res & Dev, Oslo, Norway
[2] Univ Bergen, Norwegian Back Pain Network, Res Unit, Bergen, Norway
[3] Haukeland Hosp, Outpatient Spine Clin, Dept Phys Med & Rehabil, N-5021 Bergen, Norway
[4] Univ Bergen, Fac Med, Dept Publ Hlth & Primary Hlth Care, Sect Physiotherapy Sci, Bergen, Norway
[5] Norwegian Back Pain Network, Commun Unit, Oslo, Norway