Heymans 2006.

Methods	RCT
Participants	299 participants. 1. Back School (low‐intensity) group n = 98. 2. Back School (high‐intensity) group n = 98. 3. Usual care group n = 103. Inclusion criteria: workers; non‐specific low back pain; being sick‐listed (completely or partially) between 3 and 6 weeks; age 18 to 65 years; and ability to complete written questionnaires in the Dutch language. Exclusion criteria: sick‐listed due to low back pain less than 1 month before the onset of the current episode of sick‐leave; specific pathology; pregnancy.
Interventions	1. Back School (low‐intensity) group: 4 sessions x 120 minutes for 4 weeks. 2. Back School (high‐intensity) group: 16 sessions x 60 minutes for 8 weeks. 3. Usual care group: Participants allocated to this group received usual care provided by the occupational physician according to the Dutch guidelines for the occupational health management of patients with low back pain. After 12 weeks of continued sick‐leave, the occupational physician was advised to refer the worker to more intensive interventions such as Back Schools or a multidisciplinary rehabilitation programme.
Outcomes	1. Pain: visual analogue scale. 2. Disability: Roland‐Morris Disability Questionnaire. 3. Return to work: defined as the duration of work absenteeism in calendar days from the first day of sick‐leave until full return to own work or other work with equal earnings for at least 4 weeks without (partial or full) dropout. 4. Adverse events: reported by the physiotherapists on standardised forms.
Notes	Secondary care setting. Funding: The Netherlands Organisation for Health Research and Development (ZonMw), Dutch Ministries of Health, Welfare and Sports and of Social Affairs and Employment.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Using sealed, opaque envelopes, coded according to a computerised random number generator, participants were randomly allocated to either the low‐intensity Back School, high‐intensity Back School, or usual care group.
Allocation concealment (selection bias)	Low risk	Using sealed, opaque envelopes, coded according to a computerised random number generator, participants were randomly allocated to either the low‐intensity Back School, high‐intensity Back School, or usual care group.
Blinding of participants and personnel (performance bias) All outcomes	High risk	Occupational and family physicians and physiotherapists were not blinded for the allocated intervention.
Blinding (performance bias and detection bias) All outcomes	High risk	Occupational and family physicians and physiotherapists were not blinded for the allocated intervention.
Blinding of outcome assessment (detection bias) All outcomes	Low risk	An independent research assistant extracted the work absence data.
Incomplete outcome data (attrition bias) All outcomes	Low risk	The percentage of withdrawals and dropouts was within the acceptable rate (less than 20%).
Intention‐to‐treat Analysis	Low risk	"Applying the intention‐to‐treat (ITT) principle, we included all patients in the analysis according to the group determined at randomisation."
Selective reporting (reporting bias)	Low risk	It was clear that the published report included all expected outcomes.
Similarity of baseline characteristics?	Low risk	Participants did not differ in baseline characteristics.
Co‐interventions avoided or similar?	Unclear risk	Not mentioned
Compliance acceptable?	Low risk	Compliance was acceptable based on the reported intensity/dosage, duration, number, and frequency for both the intervention and control groups.
Timing outcome assessments similar?	Low risk	All important outcomes assessments for both groups were measured at the same time.