Methodological issues in the study of personality and psychiatric state in rheumatoid arthritis.

Many studies of personality and psychiatric state among patients with rheumatoid arthritis (RA) suffer from methodological weaknesses. This review considers these weaknesses, and suggests criteria that should be met for the sound design of studies that are intended to demonstrate a role for personality traits and psychiatric states in the aetiology and course of the disease. These criteria include the method used to diagnose RA, sample size, the appropriateness of the tests of personality and psychiatric state for use with RA, and the matching of RA subjects with controls.