Botvin 1999.

Methods	Country: USA Site: 29 New York junior high schools. Focus: Reduction in tobacco and motivation to use substances by providing knowledge and skills to resist tobacco, alcohol and drugs. Design: Cluster RCT (Group 1: never smoking prevention cohort).
Participants	Baseline: 2690 Age: 7th grade (11 ‐ 12). Gender: 100% F Ethnicity: 60% A‐A, 23% H, 7% A, 3% W, 2% N‐A, 5% biracial or other. Baseline smoking data: 19% lifetime prevalence, 4% 30‐day prevalence; nonsmokers: intervention N = 1005, control N = 726.
Interventions	Category: Social Influences and social competence vs control. Programme deliverer: Teachers (received one‐day training workshop) Intervention: 15 session LST Programme, with cognitive‐behavioural skills to enhance assertiveness, resist advertising pressures, manage anxiety, communicate effectively, develop strong interpersonal relationships, and problem‐specific skills related to drug use influences, including assertiveness skills for use in situations in which students experience pressure from peers to smoke, drink or use drugs. The programme was modified for minority group use by changing the examples and the situations used for the behavioural exercises. They received 10 boosters the following year. Control: Received 10 sessions of an information‐only drug programme + 3 boosters the following year.
Outcomes	Smoking was defined as a 9‐point index from 1 (never) to 9 (more than 1 a day), and CO samples were collected at pre‐ and post‐test. Follow‐up: During grade 8 (approximately 1 yr).
Notes	Quality of intervention delivery: Project staff randomly monitored how much of the material was implemented by the teachers, and assigned an implementation score (material covered in full by 55%), which was used as a covariate in the ANCOVA. Statistical quality: Was a power computation performed? No. Was an intention‐to‐treat analysis performed? Not stated. Was a correction for clustering made? Not stated. Were appropriate statistical methods used? X² and GLM ANCOVA were used to compare the experimental and control groups.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	"Each of 29 participating junior high schools was randomly assigned to either receive the psychosocial prevention program or to serve as controls". E‐mail from Dr Botvin 29 January 2012: randomisation by computer. Clusters: Schools. Cluster constraint: Not stated. Baseline comparability: At baseline the intervention group differed from the control in higher % black (P < 0.001), higher % receiving free lunches (P < .0.001), lower grades (P < 0.02).
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	2,690 at baseline in 7th grade, 2209 (82%) in 8th grade; smokers had higher attrition rates (P < 0.0001), but there was no differential attrition across groups.
Selective reporting (reporting bias)	Low risk	No selective reporting