Examining scale discriminability in the BDI and CES-D as a function of depressive severity.

Abstract

Scale discriminability is the ability of a measure to discriminate among individuals ordered along some continuum, such as depressive severity. We used a nonparametric item-response model to examine scale discriminability in the Beck Depression Inventory (BDI) and Center for Epidemiologic Studies Depression Scale (CES-D) in both college and depressed outpatient samples. In the college sample, the CES-D was more discriminating than the BDI, but a standard CES-D cutoff score of 16 overestimated the likely prevalence of depression (45%). The CES-D may be more effective than the BDI in detecting differences in depressive severity in college students but may be less specific. In the depressed outpatient sample, the CES-D was again more discriminating than the BDI. The superior scale discriminability of the CES-D offers one explanation for its poorer specificity in college samples. Endorsing many items that discriminate at low levels of depressive severity can result in scores that exceed a cutoff criterion.