The factor structure of attention-deficit/hyperactivity disorder in schoolchildren

This study investigated the factor structure of attention-deficit/hyperactivity disorder (ADHD) by comparing the fit of a single-factor model, a correlated model with two or three factors, and a bifactor model with one general and two or three specific factors. Different three-factor solutions that varied with regard to the specification of the item “talks excessively” as impulsivity or hyperactivity were also tested. Parent ratings on the ADHD-Rating Scale (ADHD-RS-IV) were collected in a sample of 2044 schoolchildren (1st to 3rd grade) from the general population and in a clinical sample of 165 children and adolescents with ADHD referred to a public regional child and adolescent psychiatric hospital. Confirmatory factor analyses found a satisfactory fit for most models in both samples. However, a correlated three-factor model where “talks excessively” was included as an indicator of impulsivity and especially the bifactor version of this model with one general and three specific factors fit the data slightly better in the general population. In the clinical sample, a number of models performed equally well (the same version of the correlated three-factor model and all the bifactor models). Overall, the factor structure of ADHD seems to be better characterized by a bifactor model with a strong general factor and two or three weaker specific factors. Due to the strong general factor, we suggest emphasizing the ADHD-RS-IV total score rather than the subscale scores in clinical practice.