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

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.