Although studies have suggested a strong overlap between social anxiety disorder and depression, this is the first study to examine the ability of commonly used measures to differentiate symptoms of these disorders in a sample of clients with social anxiety disorder. Structural equation modeling revealed that commonly used measures of social anxiety and depression can differentiate the two constructs, rather than simply reflecting a single construct of overall distress. Logistic regression analyses indicated that scores on depressive symptom measures could predict which socially anxious clients met criteria for a comorbid depressive disorder.
A number of studies have noted the lack of discriminant validity traditionally found among measures of anxiety and depression (for a review, see Gotlib & Cane, 1989). Given this, Clark and Watson (1991) proposed the tripartite model of anxiety and depression in which they predicted that certain symptom clusters that would be relatively unique to anxiety and to depression as well as symptoms that would be common to both disorders or emotional states. Specifically, they suggested that both anxiety and depression would be characterized by negative affect and that symptoms of physiological arousal would be relatively unique to anxiety whereas symptoms of anhedonia or low positive affect would be relatively unique to depression. Despite general support for the tripartite model (e.g., Brown, Chorpita, & Barlow, 1998; Joiner, 1996; Joiner, Cantanzaro, & Laurent, 1996; Watson et al. (1995a) and Watson et al. (1995b)), there is evidence that social anxiety disorder, as well as depression, may be characterized by anhedonia (Brown et al., 1998; Watson, Clark, & Carey, 1988), suggesting that measures of anhedonia or low positive affect may not differentiate the two disorders.
Given the high degree of symptom and diagnostic comorbidity between social anxiety and depression (Alpert et al., 1999; Alpert, Maddocks, Rosenbaum, & Fava, 1994; Kessler et al., 1996; Kessler, Stang, Wittchen, Stein, & Walters, 1999; Schneier, Johnson, Hornig, Liebowitz, & Weissman, 1992; Van Ameringen, Mancini, Styan, & Donison, 1991; Zimmerman, McDermut, & Mattia, 2000), it is important for researchers to be able to validly discriminate between the two disorders. Specifically, it is important to determine whether measures of social anxiety and depressive symptoms assess the constructs of interest rather than simply assessing shared symptoms of negative affect.
The goal of this study, therefore, was to determine whether commonly used measures of social anxiety and depression can be used to differentiate the two constructs in a sample of clients with social anxiety disorder. Specifically, we used structural equation modeling to test a model in which social anxiety and depression were specified as separate constructs versus one in which they were specified as a single construct, representing overall general distress. We then examined the ability of the depressive symptom measures to predict which clients met criteria for a comorbid depressive disorder.
