Table 1.

Characteristics of the study population in the survey of 2005 and 2009

	2005 n (%)	2009 n (%)
	N = 1,854	N = 2,088
Gender
Boys	958 (51.7)	1,023 (49.0)
Girls	896 (48.3)	1,065 (51.0)
Age (years) a
13	654 (35.3)	622 (29.8)
14	342 (18.4)	316 (15.1)
15	525 (28.3)	753 (36.1)
16	333 (18.0)	397 (19.0)
Level of education
Low VMBO	773 (41.7)	825 (39.5)
High HAVO/VWO	1081 (58.3)	1,262 (60.5)
Ethnicity
Western	1,661 (89.7)	1,872 (89.7)
Non-western	191 (10.3)	215 (10.3)

^acompared with Chi-squared test (p <0.05)