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PRISMA study flow diagram of search results
Figures and Tables -
Figure 1

PRISMA study flow diagram of search results

Risk of bias graph: review authors' judgements about each risk of bias item presented as percentages across all included studies
Figures and Tables -
Figure 2

Risk of bias graph: review authors' judgements about each risk of bias item presented as percentages across all included studies

Risk of bias summary: review authors' judgements about each risk of bias item for each included study
Figures and Tables -
Figure 3

Risk of bias summary: review authors' judgements about each risk of bias item for each included study

Comparison 1 Incentive versus control. Randomized and non‐randomized controlled studies (adjusted for clustering), Outcome 1 Smoking uptake at longest follow‐up (RR).
Figures and Tables -
Analysis 1.1

Comparison 1 Incentive versus control. Randomized and non‐randomized controlled studies (adjusted for clustering), Outcome 1 Smoking uptake at longest follow‐up (RR).

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)

Crone 2003

556 intervention; 420 control (data from authors)

112 intervention; 88 control

 

 

19 months

Smoking = current smoking, including daily/weekly/experimental

Not biochemically verified

Not reported at 19 months in published paper.

Our reanalysis: RR 0.92 (95% CI 0.53 to 1.61)

Not reported

Isensee 2012a

430 never‐ smokers in intervention; 610 never‐smokers in control (data from authors)

136 intervention; 184 control

19 months

Smoking = ever smoking, even just a puff

Not biochemically verified

From published paper: Authors reported that no group differences were found in the frequency of smoking initiation but data not presented in paper.

Our reanalysis:  RR 1.05 (95% CI 0.80 to 1.38)

Bullying (Hanewinkel 2010):  "When compared with control classrooms on all three dependent variables – being victimised, active bullying or being isolated – the adjusted ORs indicated no significant differences at post‐test for any of the IGs [Intervention Groups]".

Schulze 2006

591 never‐smokers in intervention; 449 never‐smokers in control

224 intervention; 173 control

24 months

Smoking = current smoking, including irregular (less than weekly) smoking

Not biochemically verified

From published paper: 62.1% remained ‘never smoker’ in intervention group at follow‐up versus 61.4% in control group: OR 1.02 (0.83 to 1.24) adjusted for age, sex and school type.

 

Our reanalysis:  RR 0.98 (95% CI 0.77 to 1.24)

Not reported

Figures and Tables -
Analysis 2.1

Comparison 2 Results of included studies, Outcome 1 Results table: RCTs.

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

Figures and Tables -
Analysis 2.2

Comparison 2 Results of included studies, Outcome 2 Results table: non‐randomized CTs.

Smokefree Class Competitions (SFC) for preventing smoking uptake

Patient or population: Children and adolescents aged 5 ‐ 18 years who were non‐smokers at baseline

Settings: Schools in Germany, the Netherlands, Finland, Switzerland, Canada and the United States

Intervention: Participation in SFC

Comparison: No participation in SFC

Outcomes

Illustrative comparative risks* (95% CI)

Relative effect
(95% CI)

No of Participants

Actual number/

effective number2
(studies)

Quality of the evidence
(GRADE)

Assumed risk1

Corresponding risk

Smoking uptake at longest follow‐up (RCTS)

317 per 1000

320 per 1000

RR 1.00 (0.84 to 1.19)

3056/1108

(3)

Low3, 4

Smoking uptake at longest follow‐up

(Non‐RCTs)

158 per 1000

132 per 1000

RR 0.82 (0.63 to 1.08)

4219/1377

(3)

Very low3, 5, 6

*The basis for the assumed risk (e.g. the median control group risk across studies) is provided in footnotes. The corresponding risk (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI).
CI: Confidence interval; RR: Risk Ratio; RCT: Randomised Controlled Trial

GRADE Working Group grades of evidence
High quality: Further research is very unlikely to change our confidence in the estimate of effect.
Moderate quality: Further research is likely to have an important impact on our confidence in the estimate of effect and may change the estimate.
Low quality: Further research is very likely to have an important impact on our confidence in the estimate of effect and is likely to change the estimate.
Very low quality: We are very uncertain about the estimate.

1'Assumed risk' calculated as risk in control groups.
2Adjusted for clustering.
3Downgraded one level due to imprecision. All studies included had a wide confidence interval.
4Downgraded one level due to risk of bias. 2/3 studies judged to be at high risk of attrition bias.
5Downgraded one level due to observational (non‐RCT) study type.
6Downgraded one level due to risk of bias. 2/3 studies judged to be at high risk of selection bias, most other bias risks unclear.

Figures and Tables -
Comparison 1. Incentive versus control. Randomized and non‐randomized controlled studies (adjusted for clustering)

Outcome or subgroup title

No. of studies

No. of participants

Statistical method

Effect size

1 Smoking uptake at longest follow‐up (RR) Show forest plot

6

Risk Ratio (M‐H, Fixed, 95% CI)

Subtotals only

1.1 RCTs

3

1108

Risk Ratio (M‐H, Fixed, 95% CI)

1.00 [0.84, 1.19]

1.2 Non‐randomized CTs

3

1377

Risk Ratio (M‐H, Fixed, 95% CI)

0.82 [0.63, 1.08]

Figures and Tables -
Comparison 1. Incentive versus control. Randomized and non‐randomized controlled studies (adjusted for clustering)
Comparison 2. Results of included studies

Outcome or subgroup title

No. of studies

No. of participants

Statistical method

Effect size

1 Results table: RCTs Show forest plot

Other data

No numeric data

2 Results table: non‐randomized CTs Show forest plot

Other data

No numeric data

Figures and Tables -
Comparison 2. Results of included studies