DIAGNOSING MAJOR DEPRESSION IN THE ELDERLY - EVIDENCE FOR RESPONSE BIAS IN STANDARDIZED DIAGNOSTIC INTERVIEWS

Recent epidemiological and family genetic studies in different countri es using standardized diagnostic interviews for mental disorders have rather consistently demonstrated considerably lower current (e.g. ECA Study: 0.9%) and lifetime (1.4%) prevalence estimates of Major Depress ion in the elderly (older than 65 years of age) as compared to younger age groups (e.g. 30-44 years: 1 year, 3.9%; lifetime, 7.5%). Some inv estigators have questioned the validity of these data and suggested al ternative interpretations. One possibility is that the complex standar dized symptom and clinical probe questions, and the required judgmenta l processes inherent in diagnostic interviews exceed the cognitive cap acity of older adults. This may result in systematic response bias. Th is paper examines the degree to which the lower prevalence estimates o f depression in the elderly are biased due to specific characteristics of the assessment strategy. Analyses of epidemiologic data from the M unich Follow-up Study (MFS), based on the Diagnostic Interview Schedul e, demonstrate that (1) older respondents report lifetime depressive s ymptoms with the same frequency as younger respondents. The additional probe questions designed to identify the degree to which symptoms wer e caused by factors other than psychological revealed that (2) the eld erly more often attribute such symptoms to physical illnesses or condi tions. This results in (3) the exclusion of the reported symptoms as a basis for diagnosing depression. A laboratory study demonstrated that ''working memory capacity'' was a good predictor of this response beh avior, indicating that the complexity of the formalized questions exce eds the cognitive capacity of the elderly. Attributing symptoms to a p hysical illness or condition might be a heuristic strategy to simplify complex recall and judgment processes; the resulting answer is plausi ble but incorrect. We recommend that the symptom and probe questions o f standardized diagnostic interviews be simplified, especially for use with the elderly.