Study designs of evaluations included in the review
Studies that randomly allocated the unit of evaluation (students, classes or districts) and followed up students from time of intervention to at least 12th grade or age 18 years, at least one year after completion of the intervention, were eligible for inclusion.
Specific interventions included in the review
Studies of school-based smoking prevention were eligible for inclusion. The included studies evaluated various types of interventions and most were based on the social influence model. Some interventions were reported as teen, adult or teacher led. The duration of the interventions ranged from 1 to 8 years and the intensity ranged from 5 to 65 sessions; some studies also used booster sessions. None of the studies included community or media programmes.
Participants included in the review
Studies of school-based students were eligible for inclusion. Most of the studies targeted middle-school students (3rd to 10th grade); others targeted high-school students (11th grade).
Outcomes assessed in the review
Studies that measured smoking prevalence as a primary outcome were eligible for inclusion. The primary review outcome chosen was current smoking prevalence, defined as at least one cigarette in the past month. For studies that did not use this definition, other smoking outcomes chosen were monthly or daily prevalence and 'experimenter' (smokes less than once per week).
How were decisions on the relevance of primary studies made?
Three reviewers selected studies for inclusion. Two were blinded to the journal citation and article text other than the methods section.