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.