Background: Patient self-assessment instruments are useful in screening, tracking, and documenting the course of depressive symptoms with minimal clinician time. Two popular instruments are the Beck Depression Inventory (BDI-II) and the Patient Health Questionnaire (PHQ-9). We compared the performance of these two instruments in a mood disorders setting.
Methods: A retrospective study of 625 patients who completed a PHQ-9 and BDI-II as part of routine clinical care (1) during initial outpatient evaluation between 2008 and 2009, and (2) on admission to an inpatient mood disorders unit between 2006 and 2009. Pearson correlation coefficients for total PHQ-9 and BDI-II scores were calculated for all patients, the outpatients, and the inpatients.
Results: Overall r=0.77, indicating strong correlation, more in the outpatients (n=287, r=0.81) than the inpatients (n=338, r=0.67). Mean PHQ-9 and BDI-II scores for the outpatients were 15.1 (SD 7.4) and 27.8 (SD 14.1) corresponding to "moderately severe" and "moderate" categories respectively; for inpatients, 18.9 (SD 5.7) and 33.8 (SD 11.5) corresponding to "moderately severe" and "severe."
Limitations: Retrospective design and no monitoring of which instrument was completed first in case that influenced patient response to the second instrument
Conclusions: PHQ-9 and BDI-II scores, as continuous but not categorical variables, in a mood disorders subspeciality setting are closely correlated and essentially interchangeable. There are practical applications to our findings, as the PHQ-9 is shorter and free.
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