Clinical vs. self-report versions of the quick inventory of depressive symptomatology in a public sector sample.

OBJECTIVES: Recent work using classical test theory (CTT) and item response theory (IRT) has found that the self-report (QIDS-SR(16)) and clinician-rated (QIDS-C(16)) versions of the 16-item quick inventory of depressive symptomatology were generally comparable in outpatients with nonpsychotic major depressive disorder (MDD). This report extends this comparison to a less well-educated, more treatment-resistant sample that included more ethnic/racial minorities using IRT and selected classical test analyses.
METHODS: The QIDS-SR(16) and QIDS-C(16) were obtained in a sample of 441 outpatients with nonpsychotic MDD seen in the public sector in the Texas Medication Algorithm Project (TMAP). The Samejima graded response IRT model was used to compare the QIDS-SR(16) and QIDS-C(16).
RESULTS: The nine symptom domains in the QIDS-SR(16) and QIDS-C(16) related well to overall depression. The slopes of the item response functions, a, which index the strength of relationship between overall depression and each symptom, were extremely similar with the two measures. Likewise, the CTT and IRT indices of symptom frequency (item means and locations of the item response functions, b(i) were also similar with these two measures. For example, sad mood and difficulty with concentration/decision making were highly related to the overall depression severity with both the QIDS-C(16) and QIDS-SR(16). Likewise, sleeping difficulties were commonly reported, even though they were not as strongly related to overall magnitude of depression.
CONCLUSION: In this less educated, socially disadvantaged sample, differences between the QIDS-C(16) and QIDS-SR(16) were minor. The QIDS-SR(16) is a satisfactory substitute for the more time-consuming QIDS-C(16) in a broad range of adult, nonpsychotic, depressed outpatients.