The nature and measurement of depression

The initial goal of this study was to determine if the cognitive and affective components of depression, which are measured collectively by the BDI Cognitive-Affective subscale, could be identified as separate factors in a non-clinical population. A pool of 40 cognitive and affective depression items was adapted from the BDI and three other widely used depression measures. These items were administered with both state and trait instructions to 251 university students, who also responded to the BDI, Zung, CES-D, and trait measures of anxiety, anger and curiosity. Contrary to the expected finding of cognitive and affective factors, two very strong factors were identified, which were defined by items that described the presence or absence of state and trait depression. The best depression-present (dysthymia) and depression-absent (euthymia) items were selected to form 20-item State (S-Dep) and Trait (T-Dep) Depression scales, each with 10-item S-Dep and T-Dep Dysthymia and Euthymia subscales. The alpha coefficients for the S-Dep and T-Dep scales and subscales for the total sample, and in separate analyses for females and males, were .90 or higher (mdn. r = .93), indicating strong internal consistency. The T-Dep Scale correlated highly with the BDI, Zung and CES-D (mdn. r = .80), providing impressive evidence of concurrent validity. The correlations of the T-Dep Scale with all three widely used depression measures were also substantially higher than the corresponding correlations of the S-Dep Scale (mdn. r = .66). These findings suggested that while the BDI, Zung and CES-D measure both state and trait depression, they appear to more accurately assess relatively persistent trait-like characteristics.