Diffusion of effects of the ASSIST school-based smoking prevention intervention to non-participating family members: a secondary analysis of a randomized controlled trial.

AIMS: To investigate whether effects of the ASSIST (A Stop Smoking In Schools Trial) school-based smoking prevention intervention diffused from students to the people they lived with. DESIGN: Secondary analysis of a cluster-randomized control trial (cRCT). SETTING: England and Wales. PARTICIPANTS: A total of 10 730 students aged 12-13 years in 59 schools assigned using stratified block randomization to the control (29 schools, 5372 students) or intervention (30 schools, 5358 students) condition. INTERVENTION AND COMPARATOR: The ASSIST intervention involves 2 days of off-site training of influential students to encourage their peers not to smoke during a 10-week period. The control group continued with their usual education. MEASUREMENTS: The outcomes were the proportion of students who self-reported living with a smoker and the smoking status of each resident family member/caregiver. Follow-up assessments were immediately after the intervention and at 1 and 2 years post-intervention. FINDINGS: The odds ratio (OR) for living with a smoker in the intervention compared with the control groups was 0.86 [95% confidence interval (CI) = 0.72, 1.03] immediately after the intervention, OR = 0.84 (95% CI = 0.72, 0.97) at a 1-year follow-up and OR = 0.86 (95% CI = 0.75, 0.99) at 2-year follow-up. In a three-tier multi-level model with data from all three follow-ups, student-reported smoking by fathers (OR = 0.90, 95% CI = 0.80, 1.00), brothers (OR = 0.78, 95% CI = 0.67, 0.92) and sisters (OR = 0.80, 95% CI = 0.69, 0.92) was lower in the intervention compared with control group. Subgroup analyses by baseline smoking status suggested that these effects were more consistent with prevention of uptake than prompting cessation. CONCLUSIONS: A Stop Smoking In Schools Trial (ASSIST) school-based smoking prevention intervention may have reduced the prevalence of smoking in people who lived with ASSIST-trained students. This indirect transmission is consistent with the predictions of diffusion of innovations theory which underpins the design of ASSIST.