Hierarchical organization of axis I psychiatric disorder comorbidity through age 30.

Hierarchical models of psychopathology based on substantial numbers of lifetime diagnostic categories have not been sufficiently evaluated, even though such models have relevance for theories of disorder etiology, course, or prognosis. In this research, a hierarchical component model of 16 Axis I disorders is derived, and model elements are evaluated in terms of their ability to demonstrate distinct associations with several clinically-relevant variables. Participants were 816 randomly selected adolescents from the community who were repeatedly assessed for psychiatric disorders and associated risk and protective factors over a 14-year period. First-degree relatives were also interviewed to establish their lifetime psychiatric history. Patterns of lifetime comorbidity among 16 psychiatric disorders were described at five levels of organization. In addition to the broadest level that accounted for the most variance in disorder covariation, evidence was obtained at successive levels in the hierarchy for internalizing and externalizing broad-band domains that could be subdivided into more refined clusters. The validity and potential utility of the resultant hierarchical model were further supported by distinct associations that components at each level had with exposure to childhood adversities, psychiatric disorders among first-degree relatives, and psychosocial functioning at ~age 30. A large number of DSM Axis I disorders can be described within broad-band internalizing and externalizing domains, and further differentiation within these domains is possible and likely useful for some purposes. Implications of this research for conceptualizing relations among psychiatric disorders are discussed.