Table 4.

Characteristics at the baseline survey

Baseline characteristics	Group				Difference
	Intervention (n=1685)		Control (n=1759)
	N/M (SD)	%	N/M (SD)	%
Gender
Boys	866	51.5	926	52.7	χ2(1)=0.5, p=0.48
Girls	816	48.5	831	47.3
Age	10.38 (0.60)		10.35 (0.58)		t(3433)=1.27, p=0.21
School type
Gymnasium	620	36.8	771	43.7	χ2(1)=17.7, p=0.001
Others	1065	63.2	988	56.3
Yes	372	22.3	409	23.3
Immigration background
No	1291	77.7	1343	76.7	χ2(1)=0.46, p=0.50
Socioeconomic status*	4.44 (1.10)		4.44 (1.08)		t(3439)=0.01, p=0.99
Lifetime smoking
None	1575	94.4	1629	93.6
Only a few puffs	51	3.1	63	3.6	χ2(4)=2.6, p=0.63 ICCCl=0.02 ICCSch=0.03
1–19 cigarettes	37	2.2	40	2.3
20–100 cigarettes	5	0.30	5	0.29
>100 cigarettes	1	0.06	4	0.23
Current smoking
No	1657	98.8	1724	98.6	χ2(1)=0.2, p=0.65 ICCCl=0.01 ICCSch=0.01
Yes	21	1.2	25	1.4
Lifetime alcohol consumption
No	1089	65.4	1107	63.7	χ2(1)=1.1, p=0.30 ICCCl=0.05 ICCSch=0.02
Yes	576	34.6	631	36.3
Lifetime alcohol consumption without parents' knowledge
No	1603	96.0	1673	96.1	χ2(1)=0.1, p=0.81 ICCCl=0.09 ICCSch=0.02
Yes	67	4.0	67	3.9
Current alcohol consumption (‘in the last 30 days’)
Never	1572	94.1	1642	94.4	χ2(2)=1.6, p=0.44 ICCCl=0.01 ICCSch=0.004
On 1–2 days a month	85	5.1	77	4.4
≥3 days a month	14	0.8	20	1.2

^*Socioeconomic status was measured by Family Affluence Scale²⁹; sum of two items (range 0–3, a higher mean represents a higher socioeconomic status).

Cl, classes; Sch, school.