A psychometric evaluation of the clinician-rated Quick Inventory of Depressive Symptomatology (QIDS-C16) in patients with bipolar disorder.

The clinician-rated, 16-item Quick Inventory of Depressive Symptomatology (QIDS-C16) has been extensively evaluated in patients with major depressive disorder (MDD). This report assesses the psychometric properties of the QIDS-C16 in outpatients with bipolar disorder (BD, N = 405) and MDD (N = 547) and in bipolar patients in the depressed phase only (BD-D) (N = 99) enrolled in the Texas Medication Algorithm Project (TMAP) using classical test theory (CTT) and the Samejima graded item response theory (IRT) model. Values of coefficient alpha were very similar in BD, MDD, and BD-D groups at baseline (alpha = 0.80-0.81) and at exit (alpha = 0.82-0.85). The QIDS-C16 was unidimensional for all three groups. MDD and BD-D patients (n = 99) had comparable symptom levels. The BD-D patients (n = 99) had the most, and bipolar patients in the manic phase had the least depressive symptoms at baseline. IRT analyses indicated that the QIDS-C16 was most sensitive to the measurement of depression for both MDD patients and for BD-D patients in the average range. The QIDS-C16 is suitable for use with patients with BD and can be used as an outcome measure in trials enrolling both BD and MDD patients.