Development and validation of the self -reported disability status scale (SRDSS) to estimate EDSS-categories

Background: Clinician-assessed Expanded Disease Status Scale (EDSS) is gold standard in clinical investigations but normally unavailable in population-based, patient-centred MS-studies. Our objective was to develop a selfreported gait measure reflecting EDSS-categories. Methods: We developed the self-reported disability status scale (SRDSS) with three categories (<= 3.5, 4-6.5, >= 7) based on three mobility-related questions. The SRDSS was determined for 173 persons with MS and validated against clinical EDSS to calculate sensitivity and specificity. Results: Accuracy was 88.4% (153 correctly classified) and weighted kappa 0.73 (0.62-0.84). Sensitivity/specificity-pairs were 94.5%/77.8%, 69.0%/94.7% and 100%/98.2% for SRDSS <= 3.5, 4-6.5 and >= 7, respectively. Conclusions: Self-reported SRDSS approximates EDSS-categories well and fosters comparability between clinical and population-based studies.