| Methods |
Controlled cluster trial, no randomization reported. Schools assigned to intervention based on agreement to participate, with non‐participating classes acting as controls and matched with participating classes based on region and age group |
| Participants |
Country: Switzerland. Canton of Berne, German‐ and French‐speaking classes, urban and rural areas. Total of 1035 participants from 71 classes ‐ 34 in participation (intervention) group, 37 in control group. All participants were in 7th or 8th grade. Mean age 13.3 years, 53.2% girls |
| Interventions |
SFC competition. Entire classes were required to commit to a contract to be smoke‐free for 6 months to win a prize |
| Outcomes |
Smoking status at baseline (Oct/Nov 2010), and follow up about 7 months later (May/Jun 2011). Self‐reported smoking status in the past 6 months, and also in past month. Smoking‐related knowledge was assessed at baseline and follow‐up. Peer smoking was also recorded at baseline |
| Notes |
Theoretical basis: Intervention based on principles of correcting social norms (i.e. correcting the common overestimation of smokers by adolescents) and fostering commitment to a social contract |
| Risk of bias |
| Bias |
Authors' judgement |
Support for judgement |
| Random sequence generation (selection bias) |
High risk |
Randomization was not possible, as classes registered of their own accord. Analysis was undertaken for a randomly selected subsample of participating and non‐participating classes. Some differences between participating classes that participated and completed the competition compared to control, and participating classes that dropped out compared to control. (Age, class atmosphere, peers who smoked) |
| Allocation concealment (selection bias) |
High risk |
No process for allocation concealment reported |
| Blinding of participants and personnel (performance bias)
All outcomes |
Unclear risk |
Not reported |
| Blinding of outcome assessment (detection bias)
All outcomes |
Unclear risk |
Not reported |
| Incomplete outcome data (attrition bias)
All outcomes |
Low risk |
Overall low attrition |
| Selective reporting (reporting bias) |
Unclear risk |
Insufficient reporting to make a judgement on prespecified outcomes |
