Hurri 1989.

Methods	RCT
Participants	N=188; Mean age (yrs): 45.8; Gender (female): 100%; Diagnosis: patients with idiopathic LBP for at least 12 months. Setting: Occupational
Interventions	(E) Instruction material of back school in written form (no actual treatment was administered) (N=93); (C) Modified Swedish back school: 6 x 60‐minutes education and exercise sessions in 3 weeks; 11 participants per group. Refresher course 2 x 60 min after 6 months (N=95);
Outcomes	Pain (graph): Pain VAS (0 to 100) at baseline, 6## and 12 mo (graph): (E) 86, 95, 89; (C) 91, 70, 78 Low Back Pain Index (0 to 20) at baseline, 6## and 12 mo (graph): (E) 18.2, 17.7, 17.5; (C) 17.8, 15.5, 16.2 Back pain‐specific functional status (graph): Oswestry LBP Disability Questionnaire (0 to 100) at baseline, 6## and 12## mo: (E) 20.5, 21.5, 21.3; (C) 19.9, 19.2, 19.4 Return to work (no data) Sick leave due to LBP: no significant differences ## (E) significantly less effective than (C) (p < 0.05).
Notes
Risk of bias
Bias	Authors' judgement	Support for judgement
Adequate sequence generation?	High risk
Allocation concealment?	High risk	C ‐ Inadequate
Blinding? All outcomes ‐ patients?	High risk
Blinding? All outcomes ‐ providers?	High risk
Blinding? All outcomes ‐ outcome assessors?	High risk
Incomplete outcome data addressed? All outcomes ‐ drop‐outs during intervention?	Low risk
Incomplete outcome data addressed? All outcomes ‐ drop‐outs during follow‐up?	Low risk
Incomplete outcome data addressed? All outcomes ‐ ITT analysis?	Low risk
Similarity at baseline characteristics?	Low risk
Co‐interventions avoided or similar?	High risk
Compliance acceptable?	High risk