Botvin 1982.

Methods	Country: USA Site: 2 suburban New York City schools (all 7th grade classes) Focus: Smoking prevention Design: Cluster RCT (Group 1: never smoking prevention cohort)
Participants	Baseline: 426 Age: 7th graders (age 12 ‐ 12). Gender: Not stated Ethnicity: W (school A 93%; school B 90%); B (2%,4%); A (3%,3%); H (2%,3%) Baseline smoking data: 74% of 374 analysable sample.
Interventions	Category: Social influences and social competence vs control. Programme deliverer: Peers (recruited from neighbouring high school, received 4 hr training workshop. Supervised by a teacher and project staff) Intervention: 12 1hr sessions over 12 weeks. Physiological effects; teenage smoking rates; LST smoking prevention programme skills (self image, self improvement, decision making, independent thinking, advertising techniques, coping with anxiety, communication skills, social skills, assertiveness); homework; a self improvement project. Control: No programme. Note: See Botvin 1980 for similar programme delivered by outside specialists and Botvin 1983 for delivery by classroom teachers.
Outcomes	Smoking: Self reported smoking (last month, and last week). Pretest smokers excluded from analysis. Saliva samples collected, 25% subsample analysed for thiocyanate. Follow‐up: 1 yr after post‐test.
Notes	Quality of intervention delivery: No process analysis of delivery of the intervention. 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.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	"Schools were randomly assigned to experimental and control conditions". Only two schools were randomised. Method of randomisation not stated. Clusters: Schools. Cluster constraint: Not applicable as only 2 schools. Baseline comparability: Not stated
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	Unclear risk	"Complete pretest and post‐test data were obtained on 357 students. Of these, 264 (74%) were classified as nonsmokers at the time of the pretest. This group represents the nonsmoking cohort that was the focus of attention over the course of the intervention and follow‐up phases of the study". 426 baseline, 357 at 3m post‐test; no data on total numbers at 1 yr follow‐up; There were 264 nonsmokers at pretest, and of these 210 were reported present at 1 yr. Complete pre‐ and post‐test data on 84%, of whom 74% were nonsmokers at the pretest.
Selective reporting (reporting bias)	Low risk	No selective reporting