Table 1.

Characteristics of the sample by sex

		Boys			Girls
	n	Mean (SD)/n (%)		n	Mean (SD)/n (%)
Parental rated ADHD-symptoms	490	9.5	5.0	403	8.4	4.7	*
Body size
At birth
Weight, kg	490	3.4	0.8	403	3.3	0.7	*
Length, cm	490	49.6	3.6	403	48.7	3.2	*
Head circumference, cm	490	35.0	2.2	403	34.3	2.1	*
BMI, kg/m2	490	13.5	1.8	403	13.5	1.8
At 5 months
Weight, kg	482	7.6	0.9	394	7.0	0.9	*
Length, cm	478	66.5	2.3	388	64.5	2.2	*
Head circumference, cm	480	43.6	1.2	391	42.3	1.1	*
BMI, kg/m2	476	17.2	1.5	388	16.8	1.5	*
At 20 months
Weight, kg	457	12.1	1.4	376	11.4	1.4	*
Height, cm	444	84.6	3.1	369	83.2	3.2	*
Head circumference, cm	459	49.4	1.4	381	48.1	1.2	*
BMI, kg/m2	440	16.8	1.4	369	16.4	1.3	*
At 56 months
Weight, kg	482	18.5	2.6	393	17.8	2.7	*
Height, cm	470	108.6	4.4	390	107.3	4.6	*
Head circumference, cm	476	52.3	1.5	392	51.0	1.3	*
BMI, kg/m2	469	15.6	1.5	387	15.4	1.5	*
Covariates
Gestational age, weeks	490	38.4	2.8	403	38.7	2.6
Admission to neonatal ward (n, %)	490	341	69.6	403	251	62.3	*
Multiple pregnancy (n, %)	490	21	4.3	403	21	5.2
Maternal smoking during pregnancy (n, %)	490			403
> 10 cigarettes/day		27	5.5		25	6.2
1-10 cigarettes/day		82	16.7		71	17.6
None		381	77.8		307	76.2
Mother's
Height, cm	490	164.4	5.4	403	164.3	5.5
Age, Years	490	29.4	5.1	403	29.4	5.0
Parental education (n, %)	490			403
I		58	11.8		48	11.9
II		171	34.9		154	38.2
III		151	30.8		107	26.6
IV		110	22.4		94	23.3
Breast fed (yes: n, %)	490	457	93.3	403	378	93.8

Note. ADHD = Attention-Deficit/Hyperactivity Disorder, BMI = Body-mass index, Parental education I = Low to IV = High, * P < 0.05.