Evaluation of the wear-and-tear scale for therapeutic footwear, results of a generalizability study

Objective: Therapeutic footwear is often prescribed at considerable cost. Foot-care specialists normally assess the wear-and-tear of therapeutic footwear in order to monitor the adequacy of the prescribed footwear and to gain an indicator of its use. We developed a simple, rapid, easily applicable indicator of wear-and-tear of therapeutic footwear: The wearand- tear scale. The aim of this study was to investigate the intra- and inter-rater reliability of the wearand- tear scale. Methods: A test set of 100 therapeutic shoes was assembled; 24 raters (6 inexperienced and 6 experienced physiatrists, and 6 inexperienced and 6 experienced orthopaedic shoe technicians) rated the degree of wear-and-tear of the shoes on the scale (range 0-100) twice on 1 day with a 4-h interval (short-term) and twice over a 4-week interval (longterm). Generalizability theory was applied for the analysis. Results: Short-term, long-term and overall intra-rater reliability was excellent (coefficients 0.99, 0.99 and 0.98; standard error of measurement (SEM) 2.6, 2.9 and 3.9; smallest detectable changes (SDC) 7.3, 8.0 and 10.8, respectively). Inter-rater reliability between professions, experience and inexperienced raters, and overall was excellent (coefficients 0.97, 0.98 and 0.93; SEM 4.9, 4.5, and 8.1; SDC 13.7, 12.4 and 22.5, respectively). Conclusion: The wear-and-tear scale has excellent intra-rater, inter-rater, and overall reliability.