The effectiveness of a web-based brief alcohol intervention in reducing heavy drinking among adolescents aged 15–20 years with a low educational background: a two-arm parallel group cluster randomized controlled trial

Table 1 Baseline characteristics at individual and cluster level

		Intervention	Control	Total sample
		(n = 318)	(n = 291)	(N = 609)
Individual characteristics
Male, n (%)		217 (68.2)	148 (50.9)	365 (59.9)
Age, M (SD)		17.2 (1.3)	17.4 (1.2)	17.3 (1.3)
Education, n (%)
	VMBO^a	65 (20.4)	36 (12.4)	101 (16.6)
	MBO^b	253 (79.6)	255 (87.6)	508 (83.4)
Readiness to change^c, n (%)		36 (11.3)	27 (9.3)	63 (10.3)
Outcomes
	Heavy drinking^d, n (%)	117 (36.8)	105 (36.1)	222 (36.5)
	Frequency of binge drinking, n (%)	205 (64.5)	181 (62.2)	386 (63.4)
	Weekly alcohol consumption, M (SD)	12.0 (13.9)	11.3 (13.5)	11.6 (13.7)
Class characteristics
Number		37	36	73
Size, M (SD)		38.6 (19.3)	37.5 (18.2)	38.1 (18.8)

Note. N number of participants, M mean, SD standard deviation. ^aVMBO: preparatory secondary vocational education. ^bMBO: secondary vocational education. ^cReadiness to change alcohol consumption was assessed through one item asking the participants which statement applied best to them. Participants were considered to be ready to change alcohol consumption when they selected “I do not drink alcohol anymore” or “I want to reduce drinking alcohol within the upcoming six months” or “I want to reduce drinking alcohol within the upcoming month” or “I have already reduced drinking alcohol, but less than six months ago”. ^dDrinking > 7 or 12 (girls/boys aged 15–16 years) or 14 or 21 (females/males aged 17–20 years) glasses of standard units of alcohol per week and/or drinking 5 or more glasses of standard alcohol units per occasion at least once per month for boys and girls aged 15–16 years and at least once per week for males and females aged 17–20 years (= binge drinking).

ISSN: 1471-2458