Attention-deficit/hyperactivity disorder overlaps substantially with externalizing disorders. Multiple pathway models of ADHD hypothesize that several factors including emotional and motivational processes and cognitive impairments contribute to the emergence of ADHD, but their relative importance and links to diagnostic presentations are debated (Castellanos et al., Reference Castellanos, Sonuga-Barke, Milham and Tannock2006 Martel, Reference Martel2009 Sergeant, Reference Sergeant2000). Dimensional analyses allow researchers to examine how symptoms of ADHD are associated with cognitive and physiological markers across the whole phenotypic continuum.ĭespite an extensive literature that documents cognitive impairment in ADHD, it is clear that ADHD symptomatology cannot be explained with reference to cognitive deficits alone (Brocki, Forslund, Frick, & Bohlin, Reference Brocki, Forslund, Frick and Bohlin2017 Castellanos, Sonuga-Barke, Milham, & Tannock, Reference Castellanos, Sonuga-Barke, Milham and Tannock2006 Martel, Reference Martel2009 Sjöwall, Roth, & Lindqvist, Reference Sjöwall, Roth and Lindqvist2013). Therefore, studies of symptom dimensions rather than discrete diagnostic entities have been advocated (Cuthbert, Reference Cuthbert2014). Attention-deficit/hyperactivity disorder symptoms are associated with negative social and educational outcomes and psychiatric comorbidity across the symptom spectrum (Holmberg & Bölte, Reference Holmberg and Bölte2014 Vogel et al., Reference Vogel, Ten Have, Bijlenga, de Graaf, Beekman and Kooij2018). In support of the dimensional view, studies have found the genetic factors that are related to ADHD as a diagnosis and to the broader phenotype to be highly similar (Demontis et al., Reference Demontis, Walters, Martin, Mattheisen, Als, Agerbo and Neale2019).

It is increasingly recognized that ADHD symptoms are continuous, with the full syndrome representing the extreme end of traits that are found in the general population (Coghill & Sonuga-Barke, Reference Coghill and Sonuga-Barke2012 Greven, Asherson, Rijsdijk, & Plomin, Reference Greven, Asherson, Rijsdijk and Plomin2011). Consequently, ADHD presentations that are characterized primarily by one of these dimensions or by both of them are acknowledged. Although these symptom dimensions are highly correlated, they are considered to be dissociable. Attention-deficit/hyperactivity disorder (ADHD) is a diagnosis that is based on the presence of two symptom dimensions, inattention and hyperactivity/impulsivity (American Psychiatric Association, 2013).

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