Results table: non‐randomized CTs
Study	Number of non‐smokers at baseline	Number of smokers at endpoint who reported not smoking at baseline	Time point	Outcome	Biological criterion	Results	Secondary outcomes (dose response, cost, harms)	Comment
Burke 1992	Not reported	Not reported	18 months	Mean (SD) score of 5‐category self‐definition of smoking and 10‐category self‐reported frequency	Salivary thiocyanate (TCN)	From published paper:  Mean TCN at follow‐up of pre‐intervention never‐smokers higher (560 mcg/mL, SD 403) versus control (514 mcg/mL, SD 424). Primary outcome for this review not available.	Not reported
Kairouz 2009	664 intervention; 915 control	93 intervention; 165 control	10 ‐ 18 months	Smoking = ever smoking, even just a puff	Not biochemically verified	From published paper: OR 0.8 (0.5 to 1.1), adjusted for age, gender, school location, social deprivation index. Our reanalysis:  RR 0.81 (95% CI 0.55 to1.20)	Intervention participants more likely than control participants to report that people “should not hang out with smokers” (14% versus 11%) and that they, themselves would “not want to be friends with a classmate who smokes” (28% versus 25%)	Concerns about misreporting of smoking status.  Note large numbers of ever‐smokers at baseline then denying ever smoking at follow‐up.  Stat sig more in intervention vs control (24% vs 16%)
Stucki 2014	544 intervention, 378 control	39 intervention, 24 control	About 7 months	Smoking = any smoking in last 6 months, even just a puff and smoking during the previous month	Not biochemically verified	From published and additional data from authors. OR for decreased smoking prevalence 0.7, CI 0.5 to 1.0	Increased smoking‐related knowledge b ‐1.0, P < 0.01
Vartiainen 1996	Not reported and not available from authors	Not reported and not available from authors	18 months	Smoking = daily smoking	Not biochemically verified	Reports only on the increase in prevalence of smoking from baseline to follow‐up. From baseline to longest follow‐up, increase by 10.8% points in Intervention group vs 11.2% points in control group: OR 1.25 (P = 0.15). Primary outcome for this review not available.	Not reported.  Except in discussion – authors report "The social pressure created by the competition process was not greatly criticised in the pupils’ answers."
Wiborg 2002	1215 intervention group; 502 control (data from authors)	207 intervention; 107 control	12 months	Smoking = 4 week prevalence of smoking	Not biochemically verified	From published paper: OR 1.36 (1.04 to 1.76), adjusted for age, sex, smoking status at baseline Our reanalysis:  RR 0.81 (95% CI 0.53 to 1.23)	Cost benefit (Hoeflymayr 2008). Cost benefit ratio: economic modelling based on estimates of reduced smoking prevalence in Intervention group and models of assumed future smoking behaviour and cessation. Not based on prevention of initiation