Table 2.

Selected cohort and within-pairs estimates between mpas and categorical diagnoses/dimensional variables (Autistic Traits, IQ)

Categorical diagnoses		Cohort estimate				Within-pairs conditional estimate				MZ only within-pair conditional estimate
		β	OR	95% CI (OR)	p value	β	OR	95% CI (OR)	p value	β	OR	95% CI (OR)	p value
ASD and MPAs
No adjustments		.25	1.29	1.00–1.66	.047	.25	1.28	.60–2.75	.529	.35	1.42	0.63–3.19	.398
Adjusted for IQ		.23	1.26	.98–1.61	.073	.16	1.18	.55–2.54	.673	.55	1.73	.47–6.45	.413
Adjusted for ADHD		.25	1.29	1.02–1.63	.032	1.00	2.71	.84–8.80	.097	1.00	2.71	.83–8.81	.097
Adjusted for other NDDs		.28	1.33	1.05–1.67	.016	1.00	2.71	.84–8.80	.097	1.00	2.71	.83–8.81	.097

Dimensional variables		Cohort estimate				Within-pairs conditional estimate				MZ only within-pair conditional estimate
		β	SE	95% CI (β)	p value	β	SE	95% CI (β)	p value	β	SE	95% CI (β)	p value
IQ and MPAs
No adjustments		− .95	.32	− 1.59 to − .32	.003	.30	.69	− 1.04 to 1.64	.665	− .15	.67	− 1.46 to 1.17	.828
SRS-2 and MPAs
No adjustments		3.02	.98	1.09 to 4.94	.002	1.49	1.80	− 2.04 to 5.02	.409	2.11	1.85	− 1.51 to 5.73	.254
Adjusted for IQ		2.28	.97	.37 to 4.18	.019	1.78	1.83	− 1.82 to 5.37	.332	1.88	1.68	− 1.41 to 5.17	.263

Cohort and within-pairs associations between ASD, autistic traits and the number of minor physical anomalies (MPAs). The cohort model estimates associations between variables while accounting for the twin correlation; the within-pairs model estimates associations after adjusting for factors shared within twins like genetics and environment. ADHD or other NDD diagnoses, as well as IQ, were used as covariates in the each of the models

MPAs minor physical anomalies, MZ monozygotic, IQ intelligence quotient, ASD autism spectrum disorder, ADHD attention–deficit/hyperactivity disorder, ID intellectual disability, NDD neurodevelopmental disorder, SRS-2 Social Responsiveness Scale-2