Cluster randomised controlled trial of expert system based on the transtheoretical ("stages of change") model for smoking prevention and cessation in schools.

OBJECTIVES To examine whether a year long programme based on the transtheoretical model of behaviour change, incorporating three sessions using an expert system computer program and three class lessons, could reduce the prevalence of teenage smoking. DESIGN Cluster randomised trial comparing the intervention to a control group exposed only to health education as part of the English national curriculum. SETTING 52 schools in the West Midlands region. PARTICIPANTS 8352 students in year 9 (age 13-14 years) at those schools. MAIN OUTCOME MEASURES Prevalence of teenage smoking 12 months after the start of the intervention. RESULTS Of the 8352 students recruited, 7444 (89.1%) were followed up at 12 months. The intention to treat odds ratio for smoking in the intervention group relative to control was 1.08 (95% confidence interval 0.89 to 1.33). Sensitivity analysis for loss to follow up and adjustment for potential confounders did not alter these findings. CONCLUSIONS The smoking prevention and cessation intervention based on the transtheoretical model, as delivered in this trial, is ineffective in schoolchildren aged 13-14.