Table 1.

Characteristics of included studies.

Study	Study Site	Study Design	n	Number with ADHD in Study	Outcome	Diagnostic Method	Type of Adjusted Factors a
							Gender	SES	Psyc. History	Prenatal	Parental Age	Exposure
Chang et al. (2014) [23]	Sweden	Cohort	1,495,543	30,674	ADHD	ICD–10	✓			✓	✓
Chudal R. et al. (2015) [20]	Finland	Case-control	49,534	10,409	ADHD	ICD–10		✓	✓	✓	✓	✓
Galera et al. (2011) [25]	Canada	cohort	2057	330	ADHD	DSM–IV	✓	✓	✓	✓		✓
Gustafsson et al. (2011) [18]	Sweden	Case-control	32,012	237	ADHD	DSM–III–R, DSM–IV	✓			✓		✓
Hvolgaard et al. (2017) [22]	Danish	Sibling cohort	943,785	12,294	ADHD	ICD–10	✓			✓	✓	✓
Janecka et al. (2019) [21]	Danish	Cohort	1,490,745	25,307	ADHD	ICD–10	✓		✓	✓		✓
Kim et al. (2020) [19]	Korea	Case-control	28,973	2112	ADHD	K–ARS	✓	✓		✓		✓
Sauver et al. (2004) [26]	America	Case-control	5701	305	ADHD	DSM–IV	✓	✓		✓
Sciberras et al. (2011) [17]	Australia	Cohort	4464	57	ADHD	DSM–IV
Silva et al. (2014) [24]	Australia	Case-control	43,062	12,991	ADHD	DSM–IV
Wang et al. (2019) [27]	America	Cohort	321,272	16,385	ADHD	DSM–IV	✓	✓	✓	✓	✓	✓

Note: SES, social–economic status. ^a Confounding represents model covariates for gender, social–economic status (parental educational level, household income), psychiatric history (parental psychiatric history), prenatal situation (birth order, birth year, birth weight, gestational age, Apgar score, history of comorbidity), parental age (adjusted maternal age for paternal age), exposure (prenatal tobacco exposure, prenatal alcohol exposure, prenatal illegal drug exposure).