Table 1.

Socio-demographic characteristics of preschool attention-deficit hyperactivity disorder (ADHD) cases and the typically developing children in the Norwegian Mother, Father and Child Cohort (MoBa), 2003–2008.

Variable	Weighted population (N = 310)		Preschool ADHD group (N = 262)		Typically developing children (N = 78)
	N	%	N	%	N	%
Birth year
2004	68	22	26	9.9	20	25.6
2005	111	36	63	24.0	30	38.5
2006	103	33.3	90	34.4	23	29.5
2007	27	8.7	83	31.7	5	6.4
Child sex
Male	176	56.9	146	55.7	42	53.8
Female	134	43.1	116	44.3	36	46.2
Child age at clinical assessment
38–41 months	208	68	157	60.4	50	64.9
42–45 months	98	32	103	39.6	27	35.1
Missing	3		2		1
Maternal age at delivery
<=20 years	3	1.1	2	0.8	1	1.3
21–30 years	163	53.3	141	53.8	40	51.9
31–40 years	134	43.6	118	45.0	35	45.5
>40 years	6	2.1	1	0.4	1	1.3
Missing	3		0		1
Maternal education
Less than college completed	78	25.2	92	35.2	19	24.4
College completed	146	47	110	42.1	34	43.6
More than college completed	76	24.6	56	21.5	22	28.2
Other education	10	3.1	3	1.1	3	3.8
Missing	0		1		0
Marital status
Single/other	10	3.4	15	5.7	3	3.8
Cohabiting	141	45.4	132	50.6	33	42.3
Married	159	51.3	114	43.7	42	53.8
Missing	0		1		0
Maternal body mass index (kg/m2)
<25 (under to normal weight)	191	62.9	169	66.5	52	67.5
25-<30 (overweight)	89	29.3	25	9.8	6	7.8
≥30 (obese)	24	7.8	60	23.6	19	24.7
Missing	7		8		1
Parity
Nulliparous	174	56.7	157	59.9	43	55.8
Multiparous	133	43.3	105	40.1	34	44.2
Missing	3		0		1
Maternal ADHD score
Not indicative of ADHD	289	94.1	226	87.3	72	93.5
Indicative of ADHD	18	5.9	33	12.7	5	6.5
Missing	3		3		1
Maternal smoking at baseline (17 weeks)
No	230	75.1	200	76.6	61	79.2
Yes	76	24.9	61	23.4	16	20.8
Missing	3		1		1