Donchin 1990.

Methods	RCT
Participants	138 participants. 1. Back School group n = 46. 2. Calisthenics exercises group n = 46. 3. Waiting‐list control group n = 46. Inclusion criteria: at least 3 annual episodes of low back pain. Exclusion criteria: not described.
Interventions	1. Back School group: 4, 90‐minute sessions during a 2‐week period plus a 5th session after 2 months. Each group of 10 to 12 participants was supervised by a physiotherapist (education and exercises for back and abdominal muscles). 2. Calisthenics exercises group: 45‐minute sessions biweekly for 3 months in groups of 10 to 12 participants (flexion and pelvic tilt exercises in order to strengthen the abdominal muscles, expanding spinal forward flexion). 3. Waiting‐list control group.
Outcomes	Disability: Oswestry Low Back Pain Questionnaire.
Notes	Occupational setting. Funding: N/A.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	After being examined, the participants were allocated to the 3 groups by a systematic random sampling method.
Allocation concealment (selection bias)	Unclear risk	The sequence generation procedure or the method of allocation were not mentioned. The title and abstract indicate that it is an RCT.
Blinding of participants and personnel (performance bias) All outcomes	High risk	No mention of any attempts to blind the participants
Blinding (performance bias and detection bias) All outcomes	High risk	No mention of any attempts to blind the care providers
Blinding of outcome assessment (detection bias) All outcomes	High risk	No mention of any attempts to blind the assessors
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	Unclear risk	Not mentioned
Selective reporting (reporting bias)	Unclear risk	It was unclear if the published report included all expected outcomes.
Similarity of baseline characteristics?	Low risk	Demographic and clinical baseline characteristics of the study population are presented in Table 1. Demographic and clinical baseline characteristics were similar for both groups.
Co‐interventions avoided or similar?	Unclear risk	There were few reported co‐interventions in the study.
Compliance acceptable?	Low risk	Based on the description of both groups, compliance was acceptable.
Timing outcome assessments similar?	Low risk	All important outcomes assessments for both groups were measured at the same time.