The current findings point to two systematic sources for this overlap. One of these pertains to elevated rates within the fear, distress, and externalizing classes of what might be termed cross-class disorders—that is, disorders evident at elevated rates (exceeding estimated probabilities of diagnosis of .1) in each of these classes. This set of disorders included major depression, social phobia, and PTSD. The other source consists of a distinctive subgroup of individuals exhibiting heightened rates of all disorders from both the internalizing and externalizing domains—i.e., the multimorbid class. Across the two study samples, individuals in this class showed: (1) high rates of all phobic disorders (agoraphobia as well as social and specific phobias) – comparable to or higher than those evident in the fear class – along with markedly higher rates of panic disorder; (2) rates of depression, dysthymia, and GAD comparable to those observed in the distress class, along with the highest rates of PTSD compared to all classes; and (3) rates of conduct disorder, alcohol dependence, and drug dependence that substantially exceeded rates in other classes aside from the
