Use of Item Response Theory Methodology to Evaluate Differences Between Bipolar and Unipolar Depression

Affecting approximately eight million people in the US, bipolar disorder represents a significant public health concern. Over 90% of individuals diagnosed with the disorder report multiple affective episodes across their lifetime, and recent data suggest that patients with bipolar disorder will remain symptomatically ill for roughly 50% of their lives. Consistent with this chronic course, bipolar illness is characterized by marked functional impairment and substantial economic burden. Of particular note, bipolar disorder is potentially fatal. In comparison to the general population, individuals with the disorder are 20 times more likely to attempt suicide, and roughly 15% of patients die from suicide. Consistent with this clinical picture, the World Health Organization (WHO) has identified bipolar disorder as one of the top 10 most important public health problems worldwide.