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EDITOR,—Paul Brennan and colleagues found that rheumatoid factor, disease lasting longer than three months, the involvement of at least two large joints, and male sex were significant predictors of radiological erosions in patients with arthritis in primary care.1 The first two findings are consistent with, but the latter two conflict with, previous data. Is this important, and why has it arisen?

Entry criteria—The authors used the American College of Rheumatology's criteria for rheumatoid arthritis. These criteria, however, were not …