Internal consistency at baseline
| Scales (item exemplification) | Cronbach's α | Number of items | Item-total correlation rit | Item difficulty Pi in % |
| Communication (“If I talk to somebody, I will not interrupt him/her”) | α=0.73 | 9 | 0.35–0.48 | 57–86 |
| Response category: 4-point scale (I do not agree–I agree) | ||||
| Self-esteem (“I sometimes think that I'm no good”) | α=0.70 | 5 | 0.25–0.60 | 60–85 |
| Response category: 4-point scale (I do not agree–I agree) | ||||
| Self-efficacy (“Whatever happens, I will handle it”) | α=0.61 | 5 | 0.26–0.41 | 58–70 |
| Response category: 4-point scale (I do not agree–I agree) | ||||
| Self-concept (“I'm aware of my strengths”) | α=0.67 | 8 | 0.27–0.42 | 55–82 |
| Response category: 4-point scale (I do not agree–I agree) | ||||
| Class climate (“We help each other”) | α=0.73 | 9 | 0.35–0.48 | 57–86 |
| Response category: 4-point scale (I do not agree–I agree) | ||||
| Bullying (“How often have you taken part in bullying (kicked, beaten) another student?”) | α=0.71 | 3 | 0.51–0.57 | 5–13 |
| Response category: 5-point scale (Never–Few times a week) | ||||
| Victimisation (“How often have you been bullied (kicking, beating) by another student?”) | α=0.78 | 3 | 0.57–0.67 | 14–22 |
| Response category: 5-point scale (Never–Few times a week) | ||||
| Smoking-related perceived risks (“I will be sick”) | α=0.76 | 6 | 0.43–0.58 | 60–78 |
| Response category: 4-point scale (Surely not–Surely yes) | ||||
| Alcohol-related perceived risks (“I will be sick”) | α=0.79 | 5 | 0.53–0.61 | 63–80 |
| Response category: 4-point scale (Surely not–Surely yes) |