Common cause versus dynamic mutualism: Insights into ADHD's common comorbidities

Contemporary classification systems differ in their conceptualization of ADHD as either an externalizing or neurodevelopmental condition, with both perspectives promoting the common cause model as an explanation of ADHD's comorbidity. An alternative theory, dynamic mutualism, proposes that ADHD's comorbidity emerges through reciprocal interactions among symptoms over time, as opposed to a common cause.

We tested the common cause and the dynamic mutualism theories in explaining the associations between aspects of ADHD (i.e., ADHD, inattention, hyperactivity/impulsivity, cognitive disengagement) and the neurodevelopmental and externalizing spectra across four waves of the Adolescent Brain Cognitive Development (ABCD) Study data (n = 11,878 youths aged 9-10 at baseline; 48% female).

Results largely supported the common cause theory in explaining the developmental links between ADHD and both the externalizing and neurodevelopmental spectra. Findings varied across ADHD subdimensions, although not substantially, with hyperactivity/impulsivity more closely linked to the externalizing spectrum and cognitive disengagement more closely linked to the neurodevelopmental spectrum.

ADHD is best conceptualized as a disorder that bridges both the externalizing and neurodevelopmental domains, rather than fitting exclusively within either category. Given the assessment structure of the ABCD Study, there was more support for the common cause model compared with dynamic mutualism.