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Should the Combined and Predominantly Inattentive Types of ADHD Be Considered Distinct and Unrelated Disorders? Not Now, at Least


Address correspondence to Benjamin B. Lahey, Department of Psychiatry (MC 3077), University of Chicago, 5841 South Maryland Avenue, Chicago, IL 60637. E-mail:


The proposal of Milich, Balentine, and Lynam in this issue that the combined and predominantly inattentive types of attention-deficit/hyperactivity disorder (ADHD) be considered distinct and unrelated disorders is well-conceived and important. Given the current state of the empirical literature on this aspect of the taxonomy of ADHD, however, their proposal can neither be accepted nor rejected at this time. Their proposal should stimulate new research that can resolve this issue. Vexing measurement issues that would make it difficult to create a stable diagnostic boundary between two such putative disorders must be addressed, however, and care must be taken to avoid creating a new diagnostic category that confuses the taxonomy of anxiety and depression.