Evaluating the Utility of Sluggish Cognitive Tempo in Discriminating Among DSM-IV ADHD Subtypes

The objective of the current study was to evaluate how the inclusion of 3 Sluggish Cognitive Tempo (SCT) symptoms in Attention-Deficit/Hyperactivity Disorder (ADHD) diagnostic criteria influences the external validity of the ADHD subtypes. The sample comprised 228 children (166 boys, 62 girls) ranging in age from 5–18 years who were referred to clinics for attentional, behavioral, and/or learning problems and diagnosed with DSM-IV ADHD (124 Combined type, 81 Inattentive type, 23 Hyperactive-Impulsive type). Parent ratings of ADHD symptoms were obtained using the Emory Combined Rating Scale (ECRS), which assesses symptoms of the common DSM-IV childhood psychiatric disorders. Regression analyses incorporating planned comparisons were conducted to examine how the inclusion of SCT symptoms affects differences among ADHD subtypes on several external validity indicators (i.e., gender, age-of-onset, and overlapping conditions). The regression analyses did not yield any significant differences in gender ratios, mean age-of-onset, or overlapping externalizing or internalizing problems when the ADHD Inattentive type was subdivided into high- versus low-SCT groups. In conclusion, the current results suggest that the inclusion of parent-reported SCT symptoms in the ADHD diagnostic criteria has limited utility for isolating diagnostically meaningful subgroups of the Inattentive type or for enhancing the external validity of the ADHD subtypes in clinic-referred samples.