Establishing a common metric for depressive symptoms: linking the BDI-II, CES-D, and PHQ-9 to PROMIS depression

Abstract

Interest in measuring patient-reported outcomes has increased dramatically in recent decades. This has simultaneously produced numerous assessment options and confusion. In the case of depressive symptoms, there are many commonly used options for measuring the same or a very similar concept. Public and professional reporting of scores can be confused by multiple scale ranges, normative levels, and clinical thresholds. A common reporting metric would have great value and can be achieved when similar instruments are administered to a single sample and then linked to each other to produce cross-walk score tables (e.g., Dorans, 2007; Kolen & Brennan, 2004). Using multiple procedures based on item response theory and equipercentile methods, we produced cross-walk tables linking 3 popular "legacy" depression instruments-the Center for Epidemiologic Studies Depression Scale (Radloff, 1977; N = 747), the Beck Depression Inventory-II (Beck, Steer, & Brown, 1996; N = 748), and the 9-item Patient Health Questionnaire (Kroenke, Spitzer, & Williams, 2001; N = 1,120)-to the depression metric of the National Institutes of Health (NIH) Patient-Reported Outcomes Measurement Information System (PROMIS; Cella et al., 2010). The PROMIS Depression metric is centered on the U.S. general population, matching the marginal distributions of gender, age, race, and education in the 2000 U.S. census (Liu et al., 2010). The linking relationships were evaluated by resampling small subsets and estimating confidence intervals for the differences between the observed and linked PROMIS scores; in addition, PROMIS cutoff scores for depression severity were estimated to correspond with those commonly used with the legacy measures. Our results allow clinicians and researchers to retrofit existing data of 3 popular depression measures to the PROMIS Depression metric and vice versa.

Figure 1

IRT cross-walk function (based on fixed-parameter calibration) and equipercentile functions with different levels of smoothing. PROMIS Depression = Depression subscale of the Patient-Reported Outcomes Measurement Information System; IRT = item response theory; EQP = equipercentile; SM = postsmoothing.

Figure 2

Test information function of each instrument (after linking) and for the combined set of four instruments considered as a whole. PROMIS = Depression subscale of the Patient-Reported Outcomes Measurement Information System; BDI-II = Beck Depression Inventory–II; CES-D = Center for Epidemiologic Studies Depression Scale; PHQ-9 = 9-item Patient Health Questionnaire.

Figure 3

Comparison of clinical cutoff scores on the PROMIS Depression metric. CES-D: 16 or higher for positive clinical depression. PHQ-9: 5–9 (mild), 10–14 (moderate), 15–19 (moderately severe), 20 or higher (Severe). BDI-II: 0–13 (minimal), 14–19 (mild), 20–28 (moderate), 29 or higher (severe). CES-D = Center for Epidemiologic Studies Depression Scale; PHQ-9 = 9-item Patient Health Questionnaire; BDI-II = Beck Depression Inventory–II; PROMIS Depression = Depression subscale of the Patient-Reported Outcomes Measurement Information System.