Latent structure of unipolar and bipolar mood symptoms

Objectives: The taxonic versus dimensional status of mood symptoms has been the subject of debate among mental health professionals. Conventional diagnostic models suggest that mood disorders are categorical; however, the inability of categorical models to adequately account for subthreshold unipolar and bipolar presentations and the heterotypic continuity of symptoms in unipolar and bipolar cases has resulted in growing support for dimensional views. The current study sought to evaluate the relative viabilities of categorical and dimensional models of mood symptoms within a taxometric framework. Methods: We examined the latent structure of mood symptoms in an epidemiological sample drawn from the Collaborative Psychiatric Epidemiological Surveys. Using three taxometric procedures (MAMBAC, MAXEIG, and L-Mode), we analyzed indicators of mania and depression created from the mood symptoms section of the survey. Results: The taxometric analyses supported a taxonic rather than dimensional structure for mania and depression. Membership in the mania and depressive taxa was associated with meeting criteria for DSM-IV lifetime manic episode and major depressive disorder, respectively. We identified a subset of 700 individuals falling into both taxa; membership in this subset was associated with lifetime bipolar disorder status. Group membership predicted designated external variables including help-seeking, family history, and duration of impairment. Within taxon and/or complement groups, severity scores still appeared to predict external variables. Conclusion: Our findings suggest that although taxonic, mood disorders possess meaningful dimensional variation.