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Use of the DSM-IV age of onset criterion for attention deficit/hyperactivity disorder in the assessment of adolescents and young adults results in under-identification of affected individuals. Consideration should be given to revising the current nomenclatures to reflect the reality of retrospective reporting errors in age of onset as well as the presence of late onset cases.

Statistically based classification methods have successfully refined ADHD into homogenous and heritable subtypes. External validity and impairment of these subtypes was examined using the Child Behavior Checklist (CBCL). We compared mean CBCL syndrome and competency t-scores across ADHD subtypes defined by latent class analysis in a sample of 1,346 individual twins from Missouri. The potential for comorbidity with conduct disorder (CD), oppositional defiant disorder (ODD), or major depression (MD) to increase impairment in specific ADHD subtypes was also examined. CBCL profiles confirm differences in severity, with more severe classes having increased syndrome scale and decreased competency scale CBCL scores. Clinically significant impairment was found for severe inattentive and combined subtypes and the mild combined subtype. Overall, the presence of comorbid CD, ODD, or MD did not result in increased ADHD subtype impairment. CBCL scores distinguish impairment in ADHD subtypes created through LCA. Comorbidity with CD, ODD, or MD does not significantly increase impairment among ADHD subtypes. The mild combined ADHD subtype represents a clinically significant but under-studied form of ADHD.

The perception of trait relationships was measured in both schizotypic and control college subjects (N = 46) by use of a similarity rating method. Schizotypic and control subjects were selected on the basis of their scores on four scales of schizotypy: Physical Anhedonia, Perceptual Aberration, Intense Ambivalence, and Somatic Symptoms. Schizotypes as a group were more variable in their ratings of trait relationships than were controls. When each scale was considered separately, only perceptual aberrators as a group were as consistent in their ratings of trait relationships as control subjects. These findings support the hypothesis that schizotypes fail to share the semantic trait structure accepted by most normal subjects and may be a possible explanation for previous findings of social deficits in schizotypes.