Multiple assessments of depressive symptoms as an index of depression in population-based samples.

The incremental validity of repeated measurements of a short depression questionnaire was examined regarding the clinical diagnosis of depression. Participants were 951 randomly selected women of around menopausal age. They completed the Edinburgh Depression Scale (EDS) at two time points, with approximately 18 months in between. At the second time point, they participated in a structured clinical interview for depression diagnosis based on the Research Diagnostic Criteria (RDC). With repeated assessments, specificity and negative predictive value (NPV) did not change much relative to a single assessment, with a specificity of 95.0% and a NPV of 91.7% at a cut-off score of 12 on the EDS. As expected, sensitivity dropped, from 87.9% to 58.8%. However, positive predictive value (PPV) increased from 42.0% to 49.1% at a cut-off of 12. When using a cut-off score of 15 on the EDS, the PPV based on both EDS measurements reached 61.8%, yielding a 25-fold probability of being a case for women scoring above 15 at both time points (OR=24.54, 95% CI=14.24-42.28). In conclusion, the 10-item EDS is a reliable, valid and valuable screening instrument. When employed repeatedly, a more stable depression may be tapped, which can be of substantial value for both epidemiological research and clinical practice.