Rasch analysis of the Oxford shoulder score in a non-surgical occupational population

Abstract

BACKGROUND: The Oxford shoulder score (OSS) questionnaire for measuring patient perception of shoulder disability, has not tested specifically in a non-surgical population and no study has assessed the OSS with modern psychometrics based on Rasch model (RM). OBJECTIVE: To assess the psychometric properties of the OSS using RM among health-care workers with shoulder disorders and to verify its interest in a non-surgical population. METHODS: In an occupational health department of a French hospital center, a retrospective review was performed of the medical records from June 2019 to October 2020. Responses to 110 questionnaires were examined from 55 subjects (97% of women). A polytomous Rasch model based on the Partial Credit Model was used. RESULTS: Overall fit was satisfactory, the reliability coefficient was high and an ascending order was observed with the 5 categories of the scale. Analysis of the residuals supports unidimensionality and the local independence assumption. Item performance remained stable across the subgroup examined (DIF measures). Scale to-sample targeting indicated a substantial floor effect, and the mildest impairments were not well discriminated. CONCLUSIONS: OSS presents good psychometric qualities. However, it does not clearly discriminate subjects presenting the lowest levels of impairment. Its use in a non-surgical population is questionable.