DSM-IV depressive symptom expression among individuals with a history of hypomania: a comparison to those with or without a history of mania.

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.