Table 1. Descriptive statistics for the subjects.

Characteristic		Total (n = 7249)		Males (n = 3634)		Female (n = 3615)		P
		n	%	n	%	n	%
Age (mean ± SD)		12.3 ± 0.52		12.3 ± 0.49		12.2 ± 0.54		0.004
Body mass index (mean ± SD)		19.4 ± 3.71		19.5 ± 4.04		19.2 ± 3.35		0.039
Family structure	Parents and grandparent(s)	4184	57.7	2091	57.5	2093	57.9	0.228
	Two parents	2673	36.9	1340	36.9	1333	36.9
	Single parent	252	3.5	112	3.1	140	3.9
	Missing	140	1.9	91	2.5	49	1.4
Father’s employment	Full time	6651	91.8	3348	92.1	3303	91.4	0.434
	Part time	31	0.4	17	0.5	14	0.4
	Not employed	61	0.8	26	0.7	35	1.0
	Missing	506	7.0	243	6.7	263	7.3
Mother’s employment	Full time	3710	51.2	1844	50.7	1866	51.6	0.424
	Part time	2182	30.1	1108	30.5	1074	29.7
	Not employed	1023	14.1	498	13.7	525	14.5
	Missing	334	4.6	184	5.1	150	4.1
Siblings	Yes	6623	91.4	3301	90.8	3322	91.9	0.957
	No	494	6.8	244	6.7	250	6.9
	Missing	132	1.8	89	2.4	43	1.2
Frequency of breakfast	Very often	6306	87.0	3210	88.3	3096	85.6	0.000
	Often	590	8.1	250	6.9	340	9.4
	Sometimes	205	2.8	91	2.5	114	3.2
	Seldom	72	1.0	38	1.0	37	1.0
	Missing	73	1.0	45	1.2	28	0.8
Frequency of physical activity	Very often	1698	23.4	1096	30.2	602	16.7	0.000
	Often	3120	43.0	1661	45.7	1459	40.4
	Occasionally	2017	27.8	732	20.1	1285	35.5
	Never	310	4.3	88	2.4	222	6.1
	Missing	104	1.4	57	1.6	47	1.3
Amount of sleep	<7 hours	1363	18.8	547	15.1	816	22.6	0.000
	7–8 hours	3161	43.6	1485	40.9	1676	46.4
	8–9 hours	2116	29.2	1215	33.4	901	24.9
	>9 hours	512	7.1	325	8.9	187	5.2
	Missing	97	1.3	62	1.7	35	1.0

SD, standard deviation.