Revisiting the latent structure of ADHD: Is there a 'g' factor?

Background: Attention-deficit/hyperactivity disorder (ADHD) is presumed to be heterogeneous, but the best way to describe this heterogeneity remains unclear. Considerable evidence has accrued suggesting that inattention versus hyperactivity-impulsivity symptom domains predict distinct clinical outcomes and may have partially distinct etiological influence. As a result, some conceptualizations emphasize two distinct inputs to the syndrome. Yet formal testing of models that would accommodate such assumptions using modern methods (e.g., second-order factor and bifactor models) has been largely lacking. Methods: Participants were 548 children (321 boys) between the ages of 6 and 18 years. Of these 548 children, 302 children met DSM-IV criteria for ADHD, 199 were typically developing controls without ADHD, and 47 were classified as having situational or subthreshold ADHD. ADHD symptoms were assessed via parent report on a diagnostic interview and via parent and teacher report on the ADHD Rating Scale. Results: A bifactor model with a general factor and specific factors of inattention and hyperactivity-impulsivity fit best when compared with one-, two-, and three-factor models, and a second-order factor model. Conclusions: A bifactor model of ADHD latent symptom structure is superior to existing factor models of ADHD. This finding is interpreted in relation to multi-component models of ADHD development, and clinical implications are discussed.