Background: The relationship between major depressive disorder (MDD) and generalized anxiety disorder (GAD) has been problematic in psychiatric nosology. We examined two research questions: First, using a data-driven approach, exploratory factor analysis (EFA), will symptoms that define MDD and GAD appear together in one factor, or are they separable into the hypothesized dimensions of the disorders? Second, using a theory-driven approach, confirmatory factor analysis (CFA), how will the structural integrity of the resulting factors compare with those of the various models that have been used to explain the relation between the symptoms?
Material/Methods: Participants (n=3303) were a general population sample of adult Kuwaitis who self-completed the DSM-IV-TR criteria-based questionnaires for MDD and GAD. Exploratory factor analysis was by principal axis factoring, with oblique rotation. Models were compared in CFA using 7 “fit” indices in AMOS-16 software.
Results: The questionnaires had adequate psychometrics. In the EFA, each questionnaire yielded 2 factors (“somatic-affective” and “cognitive”); but when the items were combined, 3 factors emerged (“somatic-affective”/“general distress: depressed”; “core anxiety”; and “cognitive-depression”). In CFA, only the (hierarchical) bifactor model and the (dimensional) model characterized by correlation of the 3 factors met the “fit” criteria.
Conclusions: Our findings have widened the cross-cultural base of the evidence that while the symptoms of MDD and GAD form separate empiric clusters, there is an overlap of symptoms, which the disorders share. The relationship between the disorders’ symptoms probably has hierarchical and dimensional elements.

Keywords: Kuwait, Models, Statistical, Factor Analysis, Statistical, Diagnosis, Differential, Depressive Disorder, Major - diagnosis, Arabs - psychology, Anxiety Disorders - diagnosis, Psychometrics - methods, Questionnaires