Psychiatric comorbidity in the Baltimore ECA follow-up study: the matrix approach.

BACKGROUND: Psychiatric comorbidity is defined as the joint occurrence of two or more mental or substance use disorders. Widespread psychiatric comorbidity has been reported in treatment and population-based studies. The aim of this study was to measure the extent and impact of psychiatric comorbidity in a cohort of the Baltimore Epidemiologic Catchment Area study. METHODS: We examined the comorbidity burden of 16 mental disorders in a cohort of 847 participants using both established and novel analytical approaches The Comorbidity to Diagnosis Inflation Ratio (CDIR), is a statistical instrument that quantifies impact of pairwise comorbid associations, both on the whole sample, as well as on each specific disorder. RESULTS: Most anxiety disorders had substantial co-occurrence with each other, as well as with Major Depressive Disorder (MDD). In addition, mood disorders had a high degree of comorbidity with Alcohol Dependence (AD). The CDIR for the whole sample was 1.32, indicating a ratio of 132 comorbidities per 100 diagnoses. The conditions with high sample prevalence were relatively less comorbid than the low prevalence conditions. Obsessive Compulsive Disorder had a comorbidity burden that was 89% greater than the overall sample. CONCLUSION: Anxiety disorders are highly interrelated, as well as highly comorbid with depression. The comorbidity phenomenon is linked to the differential prevalence of the analyzed conditions. Comorbidity frequency (most prevalent comorbid condition) appears mutually exclusive to comorbidity burden (most widely interrelated condition). While AD and MDD were the most frequently diagnosed disorders; low prevalence conditions as OCD and GAD were the most widely interrelated.