Schinke 1985c.

Methods	Country: USA Setting: 4 elementary schools, Washington state Focus: smoking and smokeless tobacco prevention Design: cluster RCT (excluded from analysis)
Participants	Baseline: 331 Age: 6th grade (11 ‐ 12 years) Gender: no data Ethnicity: no data Baseline smoking data: no data
Interventions	Category: social influences vs. information vs. control Programme deliverer: 4 pairs of graduate social workers leaders (received 40 hrs training prior to randomisation to intervention) Intervention: direct comparison of skills training and information ‐ Skills: problem solving, resistance, interpersonal pressure in addition to health information; Health information, debates, quizzes, anti smoking skits. Both interventions included films, peer testimonials and commitments to non‐smoking (duration: 8 x 50 min weekly sessions). Control: Pre‐ and post‐test only; Post‐test only.
Outcomes	Main outcome was ever‐smoking, reported as change in % between test points. Follow up: post‐test, 6m,12m and 15m
Notes	Quality of intervention delivery: no process analysis Statistical quality: Was a power computation performed? No Was an intention‐to‐treat analysis performed? Not stated Was a correction for clustering made? No Were appropriate statistical methods used? X2, analysis by dependent t‐tests.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	"By school, subjects were randomly divided into four groups..." Method of randomisation not stated Clusters: schools Cluster constraint: not stated Baseline comparability: groups similar at baseline in age and gender and parental smoking, but student smoking rates were not compared.
Allocation concealment (selection bias)	Unclear risk	No statement
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	No statement
Incomplete outcome data (attrition bias) All outcomes	Low risk	N = 331. "Subject attrition was non significantly different by condition, across measurements."; no statement of final N at 15 months.
Selective reporting (reporting bias)	Low risk	No selective reporting