Table 2. Within-individual and within-family associations between low- and high-functioning ASD and ADHD.

Cohorts	Low-functioning ASD	High-functioning ASD
	OR (95% CI)
Within individual (N Obs=1 899 654)	1.25 (1.16–1.34)	26.08 (25.35–26.83)
Full siblings (N Obs=1 829 696)	1.17 (1.03–1.32)	4.93 (4.70–5.17)
Full cousins (N Obs=5 580 328)	0.93 (0.85–1.02)	1.68 (1.62–1.75)

Abbreviations: ADHD, attention-deficit/hyperactivity disorder; ASD, autism spectrum disorders; CI, confidence interval; OR, odds ratio. ORs and 95% CI expressing the association between low- and high-functioning ASD (that is, with or without comorbid intellectual disability) and ADHD, obtained from the within-individual analysis performed in the whole sample and from the within-family analyses performed in the cohorts of full siblings and full cousins. All the estimates are adjusted for birth year and sex.