Inter-rater concordance study of the PASI (Psoriasis Area and Severity Index)

BACKGROUND: Developed in 1978, the PASI (Psoriasis Area and Severity Index) is a method to rate psoriasis severity. Since then, it has been criticized for being extremely long, complex and for yielding significantly divergent interpretations. OBJECTIVE: To determine the PASI inter-rater reliability among three independent evaluators examining the same patients. METHODS: Cross-sectional study conducted in 2007 at a psoriasis treatment center, where 20 patients were selected. The patients were evaluated by three postgraduate students of Dermatology who independently determined the PASI of each patient. The inter-rater reliability coefficient was determined by employing intraclass correlation coefficients (ICC) and Bland & Altman plots. RESULTS: An ICC of 0.729 (IC 95%: 0.440 - 0.882) showed a significant degree of concordance among evaluators. By graphic means, the Bland & Altman plot method presents concordance gap ranges. As shown in this study, narrow gap ranges indicate a good concordance degree. It was also observed that for high PASI values, wider concordance gap ranges predominate. CONCLUSION: Based on this analysis, we may conclude that the PASI is a reliable indicator of psoriasis severity because it shows significant concordance when independent evaluations are performed.