Table 1. Sample characteristics.

Variable	Total sample (n = 10288)		Main analysis sample (n = 8449)
	N (%)	Missings, n (%)	N (%)
Gender
Boys	5179 (50.34)	89 (0.87)	4158 (49.21)
Girls	5020 (48.79)		4291 (50.79)
	M (SD)	Missings, n (%)	M (SD)
Age (12–16 years old)	13.98 (0.72)	31 (0.30)	13.98 (0.72)
Socio-economic status (range: 1–5)	4.47 (0.86)	57 (0.55)	4.51 (0.82)

Notes: M = Mean, SD = Standard deviation.

Total sample: Baseline data from all participants aged 12–16 years old.

Main analysis sample: Participants with complete data (included in regression analysis).