. 2011 Nov 1;1(2):e000352. doi: 10.1136/bmjopen-2011-000352

Table 3.

Internal consistency at baseline

Scales (item exemplification)	Cronbach's α	Number of items	Item-total correlation r_it	Item difficulty P_i 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)	α=0.73	9	0.35–0.48	57–86
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)	α=0.70	5	0.25–0.60	60–85
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)	α=0.61	5	0.26–0.41	58–70
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)	α=0.67	8	0.27–0.42	55–82
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)	α=0.73	9	0.35–0.48	57–86
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)	α=0.71	3	0.51–0.57	5–13
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)	α=0.78	3	0.57–0.67	14–22
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)	α=0.76	6	0.43–0.58	60–78
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)	α=0.79	5	0.53–0.61	63–80