Parkinson's disease and depression: psychometric properties of the Beck Depression Inventory.

Although the Beck Depression Inventory (BDI) is one of the most frequently employed measures of depression in Parkinson's disease, the somatic items included in the scale raise questions about its ability to differentiate depression from manifestations of the disease. The internal consistency and validity of the BDI as a measure of depression in a sample of 119 Parkinson's disease patients and 76 controls were studied. Results from an item analysis suggested that depression in Parkinson's disease patients is not a somatic artifact. Internal consistency reliability within the Parkinson's disease group was high. The factorial validity of the BDI was confirmed in both Parkinson's disease and control subjects. The results also indicated that Parkinsonian symptoms of depression can be measured separately from symptoms of the disease. These data suggest that the BDI including the somatic items is a reliable and valid measure of depression in Parkinson's disease and control subjects.