Under-reporting bipolar disorder in large-scale epidemiologic studies

BackgroundTo investigate if the prevalence of bipolar disorder in epidemiologic studies is an underestimate, as suggested by clinical studies.MethodsWe analyzed data from 8 countries that participated in the World Mental Health Survey Initiative (n=47,552). We identified 6.8% and 18.9% of the sample who we think were screened out inappropriately (SCI) from the euphoric and irritable bipolar sections respectively. We compared them to those who were allowed to continue the section (CONT, 2.6% of the sample for euphoric; 1.0% for irritable) and to the reference group (REF, 69.5% of the sample).ResultsThe SCI group had consistently higher rates of major depression (29.1% vs. 6.4%), earlier age of onset (24.3 y vs. 32.4 y), more suicide attempts (13.3% vs. 5.9%), and more episodes (4.2 vs. 2.7) than the REF for the euphoric group. Similar findings exist for the irritable group. Also, comorbidity with anxiety, disruptive behavior disorders and substance use were much higher than the REF.LimitationsAs with all epidemiologic studies, recall bias cannot be ruled out.ConclusionsThe findings above suggest that a number of the SCI subjects belong to the bipolar group. A revision of instruments used in epidemiologic research will probably prove what clinical studies have been showing that bipolar disorder is more common than has been reported.