Measurement properties of the Disability Rating Index in patients undergoing hip replacement

Objective: The aim of this study was to establish and validate the measurement properties of the Disability Rating Index (DRI) in a population of adults undergoing hip replacement.

Methods: One hundred and twenty-six adults participating in a randomized controlled trial completed the Oxford Hip Score, Harris Hip Score, DRI and EuroQol Group-Five Dimensions (EQ-5D) questionnaires at four time points. The structural validity of the DRI was assessed using principal component analysis. Cronbach's α was used to determine the internal consistency and scale reliability was also assessed. Correlation between the DRI and the other functional and health-related quality of life scales was used to check criterion validity. DRI responsiveness was estimated and the interpretability of the scale was also assessed by checking for edge effects.

Results: Results of analyses showed that the DRI was internally consistent (Cronbach's α = 0.92), had good association with both function-specific and general health-related quality of life scores and was sensitive to change (smallest detectable change = 2.7). No evidence of edge effects was found. Furthermore, structural assessment of the DRI revealed two novel subscales representing simple tasks and difficult tasks.

Conclusions: The DRI is structurally valid, responsive and concurs with functional assessment in adults undergoing hip replacement.