Screening for major depression in private practice

Several studies have compared the 16-item self-report version of the Quick Inventory of Depressive Symptomatology (QIDS-SR16) with other depression scales, but none has used a sample of patients from a single, large, private psychiatric practice. This study compared ratings from 175 outpatients on the QIDS-SR16, the 17-item Carroll Depression Rating Scale (CDRS-SR17, a self-report modification of the Hamilton Rating Scale for Depression), and the thirteen depression items from the Symptom Check List-90 (SCL-D13). The Mini version of the Structured Clinical Interview for DSM-IV (MiniSCID) served as a "gold standard" for assessing depression.

Basic item and scale statistics were obtained using classical test theory. Dimensionalities were obtained using factor analysis. Test information functions obtained from the Samejima item response theory model provided additional reliability-like results. This model was also used to compare patients classified as depressed versus nondepressed on the basis of the MiniSCID. Additional validity information was assessed comparing: (a) ANOVA effect sizes, (b) receiver operating characteristic curves, (c) univariate logistic regression, (d) the MANOVA, and (e) multivariate logistic regression.

The QIDS-SR16 was found to be related most strongly to the MiniSCID diagnoses. The SCL-D13, however, was the most reliable of the three scales (alpha=0.91). It was the most sensitive to differences in depression for all but the most depressed patients, for whom the CDRS-SR17 was the most sensitive. The QIDS-SR16 was the most valid based on four different analyses (effect size/ANOVA, univariate logistic regression/ROC analysis, MANOVA, and multivariate logistic regression), although only slightly more so. The QIDS-SR16 was found to be unidimensional; its items cover only the nine diagnostic symptom domains used to characterize a DSM-IV-TR major depressive episode.

All three measures performed satisfactorily, but there are clearly defined advantages to using the QIDS-SR16, as, by its very design, it assesses the core symptoms of depression and does not require a clinician.