Heterogeneity in comorbidity between major depressive disorder and generalized anxiety disorder and its clinical consequences.

Major depressive disorder (MDD) and generalized anxiety disorder (GAD) are highly comorbid and, as diagnoses, problematic because they are heterogeneous, may impair functioning even in subclinical manifestations, and may not predict important external criteria as well as empirically-derived classifications. The present study employed a latent class analysis using data from National Comorbidity Survey (1990-1992) and focused on respondents who endorsed at least 1 screening question for MDD and 1 for GAD (N = 1009). Results revealed 4 symptom domains (somatic anxiety, somatic depression, psychological anxiety, and psychological depression) reflecting the heterogeneity of MDD and GAD, and 7 respondent classes. Analysis revealed that people in classes with a high prevalence of either somatic anxiety or somatic depression symptoms presented with the highest levels of disability, distress, and service utilization. Evidence also was found for clinically meaningful subthreshold comorbid conditions. Anxiety-related and depression-related symptoms can be meaningfully differentiated, but differentiating between somatic and psychological symptoms has the greatest practical significance.