The results of recent epidemiological studies have illustrated the need for further development of the psychiatric diagnostic system.79,81-89-91 There is growing dissatisfaction with the current categorical diagnostic system, which is not believed to provide a valid representation of emotional and behavior problems in youth. First, there is a growing research demonstrating that some diagnostic entities are better characterized as a spectrum.92-94 Recent studies have begun to expand the diagnostic criteria for mental disorders to collect information on the spectra of expression of particular conditions. For example, expansion of the diagnostic concept of bipolar disorder in the National Comorbidity Survey-Replication (NCS-R) demonstrated the clinical significance of the spectrum concept of bipolarity that had long been described in clinical settings.91,92,95 Second, epidemiologic studies of children show that there is pervasive comorbidity between purportedly distinct diagnostic entities. As described in the above review, few children manifest only a single disorder. Numerous efforts are underway to integrate dimensional and categorical assessments of children.96,97
