Table 1.

Demographic characteristics

	Age 6 (n = 6194)	Age 9 (n = 4884)	Age 13 (n = 4705)
Age (M, SD)	6.06 (0.47)	9.71 (0.31)	13.55 (0.39)
Sex (% female)	49.6%	50.4%	50.4%
National origin (%)
Western	71.0%	74.2%	74.2%
Non Western	28.9%	24.6%	24.8%
Missing	0.1%	1.1%	1.0%
Education (%)
Low	6.6%	4.6%	5.1%
Middle	38.4%	37.6%	36.2%
High	48.4%	51.9%	52.9%
Missing	6.6%	5.9%	5.9%
Family income (%)
< €2000 per month	21.3%	15.5%	14.2%
> €2000 per month	72.1%	70.8%	71.2%
Missing	6.7%	13.7%	14.6%