Implementation fidelity and adolescent smoking: The X:IT study-A school randomized smoking prevention trial

Assessing the actual implementation of multi-component interventions can provide important knowledge for future interventions. Intervention components may be implemented differently, knowledge about this can provide an understanding of which components are essential and therefore must be included. The aim of this study was to examine the implementation of one, two, or all three main intervention components at the individual level and to assess the association to current smoking among 13 year-olds in the X:IT study.

Data stems from a cluster-randomized controlled trial in 94 Danish elementary schools (51 intervention; 43 control schools). Implementation was measured by aspects of adherence, dose, quality of delivery, and participant responsiveness based on questionnaire data from 4161 pupils at baseline (mean-age: 12.5 years) and 3764 pupils at first follow-up eight months later. Coordinator responses from 49 intervention schools were also included. Associations between individual level implementation of the three main components and pupil smoking were examined through a 3-level logistic regression model.

Although implementation fidelity for the three main intervention components was good, only one third (38.8%) of pupils in intervention schools were exposed to full implementation of the intervention. Among these pupils odds ratio for smoking was 0.25 (95% CI: 0.15 - 0.42).

School-based programs can be very effective if carefully implemented. Future school-based smoking preventive initiatives should include multiple components, and seek to enhance implementation quality of all components.