Methodological issues in the design of a rheumatoid arthritis activity score and its cut-offs

Abstract

Olivier Collignon Centre de Recherche Public de la Santé (CRP-Santé), Competences Centre for Methodology and Statistics (CCMS), Strassen, Luxembourg Abstract: Activity of rheumatoid arthritis (RA) can be evaluated using several scoring scales based on clinical features. The most widely used one is the Disease Activity Score involving 28 joint counts (DAS28) for which cut-offs were proposed to help physicians classify patients. However, inaccurate scoring can lead to inappropriate medical decisions. In this article some methodological issues in the design of such a score and its cut-offs are highlighted in order to further propose a strategy to overcome them. As long as the issues reviewed in this article are not addressed, results of studies based on standard disease activity scores such as DAS28 should be considered with caution. Keywords: DAS28, disease activity score, penalized logistic regression, clinical prediction, modeling