Researchers identified seven clinical features that help distinguish bipolar disorder from major depressive disorder (MDD). According to Fernando Goes of the Hopkins School of Medicine in Maryland, USA, and colleagues, “The accuracy of the identification is adequate relative to clinical application.” But these distinguishing features are primarily specific to bipolar I disorder, as there are only subtle differences between bipolar II disorder and MDD. Comparing the 386 patients with bipolar I disorder in the original data to the 684 patients with MDD, the researchers found seven characteristics associated with bipolar I disorder, and the correlations remained statistically significant after multiple logistic regression analysis. The strongest correlations among these characteristics were history of euphoria after antidepressant treatment, followed by delusions, psychomotor retardation, incapacitation (incapacity), more mixed symptoms, more episodes, and shorter episode length. Analysis of subject operational characteristics showed that these seven characteristics distinguished well between bipolar I disorder and MDD, with an area under the curve of 0.84. The seven characteristics were well replicated in independent data sets of 1000 patients with bipolar I disorder and 1000 patients with MDD. The investigators reported in the journal Psychological Medicine that the sensitivity of these seven clinical features was 76% and the specificity was 78% under optimal conditions. The 158 patients with bipolar II disorder differed from those with MDD by only two characteristics: increased number of mixed symptoms and euphoric experience after antidepressant treatment. The researchers concluded that the study suggests that “clinical characteristics still have important classification potential and should not be overlooked.” The researchers recommend that “these features should be combined with biomarkers to predict diagnosis and disease course.