Longitudinal associations between depressive and anxiety disorders: a comparison of two trait models

Background. Depression and anxiety are highly co-morbid disorders. Two latent trait models have been proposed to explain the nature of the relationship between these disorders. The first posits that depressive and anxiety disorders are both manifestations of a single internalizing factor. The second model, based on a tripartite model proposed by Clark & Watson [Journal of Abnormal Psychology (1991) 100, 316-336], proposes that depressive and anxiety disorders reflect a combination of shared and disorder-specific factors. Method. We directly compared the two models in a sample of 891 individuals from the Oregon Adolescent Depression Project who participated in up to four diagnostic assessments over approximately 15 years. Structural equation models were used to examine the relationship between depressive and anxiety disorders across different developmental periods (< 14, 14-18, 19-23, 24-30 years of age). Results. The one- and three-factor models were hierarchically related. Thus, a direct comparison between the one- and three-factor models was possible using a chi(2) difference test. The result found that the three-factor model fit the data better than the one-factor model. Conclusions. The three-factor model, positing that depressive and anxiety disorders were caused by a combination of shared and disorder-specific factors, provided a significantly better fit to the data than the one-factor model postulating that a single factor influences the development of both depressive and anxiety disorders.