Table 1.

Characteristics of the cases and controls

	Cases (n = 726)		Controls (n = 1620)		Control/Case ratio	p
	n	%	n	%
Gender						ns
Male	395	54.4	892	55.1	2.3
Age at the reference date (years)						<0.01
<2	108	14.9	362	22.4	3.4
2	98	13.5	146	9.0	1.5
3–4	185	25.5	293	18.1	1.6
5–6	114	15.7	218	13.5	1.9
7–8	74	10.2	160	9.9	2.2
9–11	88	12.1	217	13.4	2.5
12–14	59	8.1	224	13.8	3.8
Number of children (0–14 years) living in the household						ns
1	226	31.1	528	32.6	2.3
2	321	44.2	688	42.5	2.1
≥3	175	24.1	404	24.9	2.3
Missing data	4	0.6	0	0.0
Birth order						<0.01
1	362	49.9	685	42.3	1.9
2	232	32.0	589	36.4	2.5
≥3	132	18.2	346	21.4	2.6
Daycare						ns
No	634	87.3	1418	87.5	2.2
Yes	92	12.7	202	12.5	2.2
Maternal educational level						ns
≤ High school	438	60.3	939	58.0	2.1
> High school	288	39.7	681	42.0	2.4
Paternal educational level						0.02
≤ High school	497	68.5	1021	63.0	2.1
> High school	222	30.6	584	36.1	2.6
Missing data	7	1.0	15	0.9
Degree of urbanization						ns
Rural	226	31.1	569	35.1	2.5
Mixed	171	23.6	367	22.7	2.1
Urban	315	43.4	658	40.6	2.1
Missing data	14	1.9	26	1.6