Why are anxiety and depressive symptoms comorbid in youth? : a multi-wave, longitudinal examination of competing etiological models

Comorbidity, defined as the manifestation of multiple disorders within an individual, has become the rule, rather than the exception. In youth, the co-occurrence of depression and anxiety is not only common, but leads to a more severe course of mental illness and poorer treatment response. Thus, researchers have aimed to understand the development of this frequent, and deleterious, relation. A collection of research points to two developmental explanations for why depression and anxiety may relate: A causal model, in which anxiety predicts depression, and a correlated liabilities model, where shared vulnerability factors predict both anxiety and depression. While promising trends have been identified for both models, a consistent pattern for the development of comorbid symptoms has yet to emerge. The present study sought to clarify past research by introducing a diathesis-anxiety approach to understanding comorbidity in youth. Specifically, we predicted that specific cognitive vulnerabilities would interact with anxiety symptoms to predict prospective depressive symptoms. For this study, 678 3rd (n=208), 6th (n=245), and 9th (n=225) grade girls (n=380) and boys (n=298) completed self-report measures at baseline assessing cognitive vulnerabilities (rumination, negative inferential styles, and self-criticism), stressors, depression, and anxiety. Every 3 months over the next 18 months, youth completed follow-up measures of depression, anxiety, and stressors. Findings supported a diathesis-anxiety approach for self-criticism (t(2494) = 3.36, p .05). These results clarify past results concerning comorbidity by suggesting that multiple pathways exist for comorbid depressive and anxiety states, and by introducing diathesis-anxiety models as an important and novel explanation for comorbid emotional distress in youth. Clinical implications and future developmental psychopathology research on this important topic are discussed.Dr.P.H.Includes bibliographical referencesby Joseph R. Cohe