Common Cause versus Dynamic Mutualism: Empirical Insights into ADHD’s Placement Within the Psychopathology Hierarchy

Abstract

Contemporary psychopathology classification systems disagree on how ADHD should be conceptualized. One system regards ADHD as an externalizing condition because it argues that it is primarily comorbid with conditions characterized by poor impulse control. Another system regards ADHD as a neurodevelopmental condition because it is primarily comorbid with conditions characterized by early onset and cognitive deficits. Despite these disagreements, both perspectives assume that ADHD’s comorbidity arises because ADHD shares a common set of causes, or shared etiology, with other forms of psychopathology. Still, emerging models posit that comorbidity arises from dynamic interactions among forms of psychopathology, a theory known as dynamic mutualism. We pitted the common cause theory against the dynamic mutualism theory in explaining the developmental ties between ADHD dimensions (i.e., ADHD, inattention, hyperactivity/impulsivity, cognitive disengagement) and three psychopathology spectra (i.e., externalizing, neurodevelopmental, internalizing). Results support the common cause theory, with the strongest evidence for the neurodevelopmental and externalizing spectra. Taken together, our findings support conceptualizing ADHD as a condition that spans both the externalizing and neurodevelopmental spectra as opposed to fitting exclusively within either category.