A new generation of comorbidity research in the era of neuroscience and Research Domain Criteria.

When the revised third edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-III-R; American Psychiatric Association [APA], 1987) was published 30 years ago, few could have anticipated the fundamental changes to psychopathology research and practice that would ensue. The DSM-III-R was released so soon after the DSM-III (APA, 1980), and contained so few changes to diagnostic criteria, that it could not be considered a fourth edition. Nevertheless, one change, elimination of exclusion criteria, altered the way that child and adult psychopathologists conceptualized, diagnosed, and even treated psychiatric disorders (see Beauchaine & Klein, in press). Exclusion criteria were used to implement diagnostic hierarchies, which aid in differential diagnosis. Because those who are afflicted with psychopathology often present with a variety of symptoms, most of which are nonspecific to any single disorder, the task of diagnosis can be formidable, and in some cases somewhat arbitrary. Diagnostic hierarchies assign certain symptoms priority over others, which simplifies diagnostic decisions. In the DSM-III, organic mental disorders were at the top of the diagnostic hierarchy, followed by schizophrenia, major mood disorders, and neurotic/personality disorders. According to this hierarchy, if an organic brain syndrome (central nervous system disease, brain trauma, or substanceinduced brain damage) was identified, diagnoses of schizophrenia, mood disorders, and neurotic/personality disorders were precluded. In the absence of organic factors, schizophrenia received priority in diagnosis, even if symptoms of mood and/or neurotic/personality disorders were present. In the absence of both organic factors and schizophrenia, mood disorder symptoms took precedence. Neurotic/personality disorder diagnoses were considered only in the absence of organic brain syndromes, schizophrenia, and mood disorders. Research conducted in the early 1980s demonstrated that for some disorders, excluding symptoms at lower levels of the diagnostic hierarchy omitted important information, with potential implications for understanding etiology and devising effective treatments (e.g., Leckman, Weissman, Merikangas, Pauls, & Prusoff, 1983). Although details of such studies are beyond the scope of this editorial, they prompted the APA to abandon diagnostic hierarchies in subsequent versions of the DSM, except when used to rule out organic (e.g., general medical or substance-induced) causes of mental disorder. It is perhaps not surprising that diagnostic hierarchies curtailed rates of comorbidity. Individuals could not be diagnosed with schizophrenia and depression, or with a mood disorder and a personality disorder. This situation changed markedly following publication of the DSM-III-R. In the subsequent decade or so, foundational articles on potential sources and subtypes of comorbidity emerged (e.g., Angold, Costello, & Erkanli, 1999; Klein & Riso, 1993), comorbidity became a major focus of study, and the National Comorbidity Survey (NCS), a congressionally mandated evaluation of DSM-III-R psychiatric disorders and their co-occurrence, was launched (Kessler et al., 1994). Understanding comorbidity has been at the top of the research agenda of mental health professionals, including developmental psychopathologists, ever since (see, e.g., Beauchaine & McNulty, 2013). The NCS, which was conducted between 1990 and 1992, indicated higher prevalence rates of psychopathology than were expected at the time. Almost 50% of respondents reported a lifetime DSM-III-R psychiatric disorder (Kessler et al., 1994), and among this group, half experienced at least one additional disorder and a third experienced three or more disorders. These findings initiated an upsurge in comorbidity research that continues to this day. More recent efforts to document patterns of comorbidity include the NCS-2, which included reinterviews of NCS respondents to evaluate the Address correspondence and reprint requests to: Theodore P. Beauchaine, Department of Psychology, The Ohio State University, 1835 Neil Avenue, Columbus, OH 43210; E-mail: [email protected]; or Dante Cicchetti, Institute of Child Development, University of Minnesota, 51 East River Road, Minneapolis, MN 55455; E-mail: [email protected]. Development and Psychopathology 28 (2016), 891–894 # Cambridge University Press 2016 doi:10.1017/S0954579416000602