Interpreting outcome measures and defining treatment success

Abstract

ORIGINAL ARTICLE, p 1326 Outcome measures research provides one of the fundamental building blocks for clinical trials throughout medicine. What defines treatment success or failure? In the process of bringing new drugs to market, disease severity scales have often been created without an initial evidence base to demonstrate validity and reliability. A classic example of this is the Psoriasis Area and Severity Index (PASI) scale, which was developed as part of a psoriasis clinical trial.1 Ideally, an outcome measure should be simple to understand, relevant to patients and clinicians, quick to perform and sensitive to change. By anchoring Patient‐Oriented Eczema Measure (POEM) scores to five patient‐assessed eczema severity bands, Charman et al.2 have further simplified the outcome measure to improve interpretation of scores. The authors asked 1000 patients with eczema to complete both a POEM score and two global anchor questions that summarized the severity of their eczema. High external validity was ensured by the inclusion of children and adults from both primary and secondary care, in both rural and urban settings. The results permitted conversion from the 28‐point POEM numerical score to five bands ranging from clear/almost clear to very severe atopic eczema. It should be remembered that severity bands may not tell the whole story because a change from one band to another may be due to only a small change in score, for example from just below to just above a band cut‐off. Fortunately, a minimal clinically important difference score of 3.4 has been established for the POEM3 and so the two parameters can be used together to permit a full interpretation of POEM score changes.