Table 2.

Univariate and multivariate logistic regressions on the associations of only-child status and pet ownership with risk of ADHD.

	Crude model		Adjusted model*
	Odds ratio	p-value	Odds ratio	p-value
Overall
Only child (yes vs. no)	1.42 (1.34–1.49)	<0.001	1.30 (1.23–1.38)	<0.001
Number of children
≥3	1.00 (reference)		1.00 (reference)
2	1.19 (1.06–1.33)	0.003	1.22 (1.09–1.38)	0.001
1	1.65 (1.47–1.86)	<0.001	1.56 (1.39–1.77)	<0.001
Pet ownership
No	1.00 (reference)		1.00 (reference)
Only during age 0–1 year	1.83 (1.49–2.22)	<0.001	1.59 (1.30–1.95)	<0.001
Only during ages 1–3 years	1.71 (1.40–2.08)	<0.001	1.58 (1.28–1.93)	<0.001
During both age ranges	1.82 (1.57–2.10)	<0.001	1.66 (1.42–1.92)	<0.001
Boys
Only child (yes vs. no)	1.44 (1.34, 1.54)	<0.001	1.33 (1.24, 1.43)	<0.001
Number of children
≥3	1.00 (reference)		1.00 (reference)
2	1.24 (1.07–1.44)	0.005	1.25 (1.08–1.46)	0.004
1	1.74 (1.50–2.02)	<0.001	1.63 (1.40–1.91)	<0.001
Pet ownership
No	1.00 (reference)		1.00 (reference)
Only during age 0–1 year	1.89 (1.46, 2.42)	<0.001	1.65 (1.26, 2.12)	<0.001
Only during ages 1–3 years	1.75 (1.34, 2.25)	<0.001	1.59 (1.21, 2.05)	<0.001
During both age ranges	1.91 (1.58, 2.29)	<0.001	1.71 (1.41, 2.06)	<0.001
Girls
Only child (yes vs. no)	1.35 (1.23, 1.47)	<0.001	1.26 (1.15, 1.39)	<0.001
Number of children
≥3	1.00 (reference)		1.00 (reference)
2	1.10 (0.92–1.33)	0.287	1.19 (0.99–1.44)	0.066
1	1.47 (1.22–1.78)	<0.001	1.48 (1.22–1.81)	<0.001
Pet ownership
No	1.00 (reference)		1.00 (reference)
Only during age 0–1 year	1.78 (1.27, 2.44)	<0.001	1.51 (1.07, 2.08)	0.014
Only during ages 1–3 years	1.76 (1.28, 2.38)	<0.001	1.57 (1.13, 2.12)	0.005
During both age ranges	1.75 (1.37, 2.20)	<0.001	1.57 (1.22, 1.99)	<0.001

*Adjusted for child age, maternal age, paternal age, maternal education, paternal education, marital status, household income, family functioning score, and child sex were additionally adjusted in the overall model.

ADHD, attention-deficit/hyperactivity disorder.