Depression scales in rheumatoid arthritis: criterion contamination in interpretation of patient responses.

Self-report depression scales include items concerning somatic symptoms, such as fatigue, pain, and inability to work, which may be symptoms of depression in individuals who do not have a chronic disease. However, in patients with somatic diseases such as rheumatoid arthritis, these symptoms may reflect disease rather than depression. Interpretation of responses to these items in patients with chronic disease as indicating depression is known as "criterion contamination". Criterion contamination has been described in responses of patients with rheumatoid arthritis on many widely-used depression scales, including the Minnesota Multiphasic Personality Inventory (MMPI), the Beck Depression Inventory, and the Center for Epidemiologic Studies Depression Index (CES-D). Evidence for criterion contamination in responses of patients with rheumatoid arthritis on these depression scales is summarized in this essay.