Table 1.

Demographic characteristic of cases and age/region-matched controls, United States and Canada, 1999–2002

Factor	Cases N=512		Controls N=509
	n	%	n	%
Gender
Male	218	42.6	270	53.1
Female	294	57.4	239	46.9
Child’s age at reference date
< 2 years	146	27.9	137	26.9
2–3years	161	31.5	141	27.7
4+ years	205	40.5	231	45.4
Geographic region
Midwest	156	30.5	152	29.9
Northeast	69	13.5	59	11.6
South	174	34	180	35.4
West	57	11.1	62	12.2
Canada	56	10.9	56	11
Mother’s race
White	384	75	398	78.2
African American	68	13.3	57	11.2
Hispanic	42	8.2	33	6.5
Other	18	3.5	21	4.1
Mother’s educationa
0–11 years	43	8.4	40	7.9
High school degree	134	26.2	114	22.4
> High school	335	65.4	354	69.7
Household incomeb
<10k	46	9.0	37	7.9
10–20k	79	15.5	96	20.4
21–30k	63	12.4	67	14.2
31–40k	65	12.6	65	13.8
41–50k	64	12.2	63	13.4
51+k	156	30.2	143	30.3
Mother’s age
<20 years	39	7.6	37	7.3
20–24 years	110	21.5	103	20.2
25–30 years	178	34.8	162	31.8
31+	185	36.1	207	40.7

^aThere was 1 missing value for a control mother’s education

^bThere were 77 missing values for household income (39 cases and 38 controls).