Abstract
In an effort to advance an understanding of the phenomenology of bipolar II depression, the current study used methods based in item response theory to evaluate differences in DSM-IV depression symptom endorsement in an epidemiological sample of individuals with a history of hypomania (i.e., bipolar II depression) in comparison to: a) individuals with a history of mania (i.e., bipolar I depression), and b) individuals without a history of hypomania or mania (i.e., unipolar depression). Clinical interview data were drawn from a subsample (n = 13,753) of individuals with bipolar II, bipolar I, or unipolar depression who had participated in the National Epidemiologic Survey on Alcohol and Related Conditions. A two-parameter item response model was used to estimate differential item functioning (DIF) between these groups. Differences in severity parameter estimates revealed that suicidal ideation/attempt was less likely to be endorsed across most levels of depression severity in bipolar II versus bipolar I disorder. There were no significant differences between groups on the remaining DSM-IV symptoms. Although preliminary, current study data are consistent with recent assertions that depression may be understood as a clinical phenomenon that is consistent across the major affective disorders. An exception to this conclusion may be in the area of suicidal ideation, which requires additional attention.