Table 1

Comparison of groups at baseline (n=3440)

Intervention group —participation, N=1161Intervention group —no participation, N=943Control group, N=1336
MSDMSDMSD
Demographics
 Age12.540.6912.730.7612.690.73
  • F(2,123)=6.52; p=0.002

  • ICCCls=0.12, ICCSchl=0.07

N%N%N%
 Gender
  Male57849.846048.866850.0χ2(2)=0.32; p=0.850
  Female58350.248351.266850.0
 Nationality
  German112297.389795.6127996.1χ2(2)=3.41; p=0.182
  Others312.7414.4523.9
Smoking behaviour
 Lifetime smoking
  • F(2,123)=4.15; p=0.018

  • ICCCls=0.07, ICCSchl=0.11

  No63555.144948.073255.2
  Just a few puffs27824.151923.427220.5
  1–19 cigarettes13211.511712.515811.9
  20–100 cigarettes524.5727.7947.1
  >100 cigarettes564.9788.3705.3
 Current smoking
  No smoking97884.372977.6109982.3
  • F(2,123)=4.95; p=0.009

  • ICCCls=0.11, ICCSchl=0.07

  Less than once a month746.4485.1725.4
  At least monthly, less than weekly272.3404.3392.9
  At least weekly, less than daily312.7333.5564.2
  Daily504.3899.5695.2
Confounders
 Sensation-seeking*1.700.381.750.421.690.40
  • F(2,123)=2.38; p=0.097

  • ICCCls=0.06, ICCSchl=0.04

 Parenting3.130.503.060.553.090.52
  • F(2,123)=2.32; p=0.102

  • ICCCls=0.03, ICCSchl=0.04

 Parent smoking
  No45939.937240.056943.2χ2(2)=0.60; p=0.743
  Any69260.155760.074856.8
 Sibling smoking
  No84974.163868.595572.2χ2(2)=2.97; p=0.227
  Any29725.929431.536727.8
 Peer smoking
  No50343.833035.355241.8χ2(4)=4.87; p=0.087
  Some52345.642345.257743.7
  Most or all12210.618219.519314.6
 Class climate
 Student’s perception2.130.492.170.482.130.47
  • F(2,123)=0.99; p=0.373

  • ICCCls=0.21, ICCSchl=0.03

 Teacher's perception§2.250.321.950.402.060.33F(2,107)=11.96; p=0.001
ICCSchl=0.00
  • * Compliance rating ranging from 1 to 4, with higher scores indicating higher levels of sensation seeking/rebelliousness.

  • Compliance rating ranging from 1 to 4, with higher values representing higher levels of parental control and responsiveness.

  • Compliance rating ranging from 1 to 4, with higher values representing a worse climate.

  • § Compliance rating ranging from 0 to 3, with higher values representing a better climate.

  • ICC, intraclass correlation or variance proportion (the student proportion is 1 minus school plus classroom ICCs); Cls, Class; Schl, School.