The ADHD response-inhibition deficit as measured by the stop task: Replication with DSM-IV combined type, extension, and qualification

Although response inhibition has been proposed as a core element of child a ttention-deficit hyperactivity disorder (ADHD), the literature is heavily r eliant on studies using DSM-III-R diagnostic criteria, older methods of mea suring response inhibition, samples of boys, and failing to control thoroug hly for comorbid problems-both as diagnoses and as subclinical variation. T he present study replicated a deficit in response inhibition in the ADHD co mbined type (DSM-IV, American Psychiatric Association, 1994) using samples matched on age and sex. The study replicated an effect size of approximatel y d = .6 in boys with ADHD, and observed an even larger effect size for gir ls, although the Sex x Group interaction was nonsignificant. Children with ADHD also had problems with response output, shown by variable responding. Excluding comorbid conduct disorder, reading disorder, generalized anxiety disorder, obsessive-compulsive disorder, major depression, and posttraumati c stress disorder from the sample did not alter the results. Correlations i ndicated that response inhibition was associated with both attentional prob lems and reading level. Covarying for reading problems did not eliminate th e ADHD group effect, but the association of response inhibition with readin g clearly requires further examination. Overall, the study supported the ro le of response inhibition in the DSM-IV ADHD combined type, but with key qu alifications as to degree of specificity in reference both to comorbid prob lems and other executive functions.