Measuring depression levels in HIV-infected patients as part of routine clinical care using the nine-item Patient Health Questionnaire (PHQ-9)

Abstract

Little is known about the psychometric properties of depression instruments among persons infected with HIV. We analyzed data from a large sample of patients in usual care in two US cities (n=1467) using the nine-item Patient Health Questionnaire (PHQ-9) from the PRIME-MD. The PHQ-9 had curvilinear scaling properties and varying levels of measurement precision along the continuum of depression measured by the instrument. In our cohort, the scale showed a prominent floor effect and a distribution of scores across depression severity levels. Three items had differential item functioning (DIF) with respect to race (African-American vs. white); two had DIF with respect to sex; and one had DIF with respect to age. There was minimal individual-level DIF impact. Twenty percent of the difference in mean depression levels between African-Americans and whites was due to DIF. While standard scores for the PHQ-9 may be appropriate for use with individual HIV-infected patients in cross-sectional settings, these results suggest that investigations of depression across groups and within patients across time may require a more sophisticated analytic framework.

Keywords:

• depression
• HIV
• item response theory
• differential item functioning

Acknowledgements

This work was presented in part at the International Conference on Outcomes Measurement, Bethesda, Maryland, September, 2008. This work was supported by grants from the Mentored Patient-Oriented Research Career Development Award NIAID Grant (AI-60464), the University of Washington Center for AIDS Research NIAID Grant (AI-27757), Improving Cognitive Outcome Precision & Responsiveness with Modern Psychometrics NIA Grant (R01 AG-029672), and the Centers for AIDS Research Network of Integrated Clinical Systems (CNICS) Grant (R24 AI067039).