Doctor of Philosophy (PhD)



Document Type



Researchers have suggested that intraindividual variability (IIV), or variation in cognitive testing performance within an individual across a measure or group of measures, may be an endophenotypic marker of Attention-Deficit/Hyperactivity Disorder (ADHD). However, not all studies have consistently demonstrated significant differences in IIV between individuals with and without ADHD. One potential explanation for this ambiguity is experimental group heterogeneity owing to Sluggish Cognitive Tempo (SCT). Individuals with SCT exhibit behavioral characteristics dissimilar from individuals with ADHD; rather than being impulsive, hyperactive, and aggressive, they tend to be shy, day-dreamy, and cognitively slow. Researchers have hypothesized that the presence of SCT in the absence of hyperactivity may reflect a distinct purely-inattentive condition that is currently diagnosed as ADHD. If these purely inattentive individuals are included in ADHD experimental groups, they could obfuscate between-groups differences. Unfortunately, few studies have attempted to separate purely inattentive individuals from those with ADHD, with none having examined cognitive functioning after such a separation and in adults. The purpose of the current study, then, was to attempt to identify and separate adults with “pure inattention” from adults with ADHD, and to then compare the groups’ performances on a large neuropsychological test battery. Of particular interest were measured group differences in IIV—operationalized as both reaction time standard deviation and intraindividual standard deviation (ISD)—and SCT as assessed by objective cognitive testing. Cluster analysis was used to identify experimental groups via responses to twelve items on the Wender Utah Rating Scale (WURS). Individuals were also grouped, in separate analyses, by DSM-IV-TR ADHD subtype, and by their degree of endorsed SCT-like symptoms on the WURS. Results indicated that the use of the selected items from the WURS, combined with cluster analysis, was not an effective method of delineating a purely inattentive group. No significant between-groups effects were identified across any of the three grouping methods with respect to IIV or SCT. The implications of these results are discussed, and future research directions are suggested.



Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Gouvier, Wm. Drew



Included in

Psychology Commons