Analysis of the psychometric properties of the American Orthopaedic Foot and Ankle Society Score (AOFAS) in rheumatoid arthritis patients: application of the Rasch model

Abstract

Objective: To tested the reliability and validity of Aofas in a sample of rheumatoid arthritis patients.

Methods: The scale was applicable to rheumatoid arthritis patients, twice by the interviewer 1 and once by the interviewer 2. The Aofas was subjected to test-retest reliability analysis (with 20 Rheumatoid arthritis subjects). The psychometric properties were investigated using Rasch analysis on 33 Rheumatoid arthritis patients.

Results: Intra-Class Correlation Coefficient (ICC) were (0.90<ICC<0.95; p<0.001) for intra-observer reliability and (0.75<ICC<0.91; p<0.001) for inter-observer reliability. Subjects separation rates were 1.9 and 4.75 for the items, showing that patients fell into three ability levels, and the items were divided into six difficulties levels. The Rasch analysis showed that eight items was satisfactory. One erroneous item have been identified, showing percentages above the 5% allowed by the statistical model. Further Rasch modeling suggested revising the original item 8.

Conclusions: The results suggest that the Brazilian versions of Aofas exhibit adequate reliability, construct validity, response stability. These findings indicate that Aofas Ankle-Hindfoot scale presents a significant potential for clinical applicability in individuals with rheumatoid arthritis. Other studies in populations with other characteristics are now underway.

Keywords: Análise Rasch; Artrite reumatoide; Avaliação; Disability; Escala; Evaluation; Incapacidade; Rasch analysis; Rheumatoid arthritis; Scale.