Rasch analysis of the Disabilities of the Arm, Shoulder and Hand (DASH) instrument in patients with a humeral shaft fracture

Background: The Disabilities of the Arm, Shoulder and Hand (DASH) instrument was developed to assess the disability experienced by patients with any musculoskeletal condition of the upper extremity and to monitor change in symptoms and upper-limb function over time. The 30 items are scored on a 5-point rating scale. The Dutch-language version of the DASH instrument (DASH-DLV) has been examined with the classical test theory in patients with a humeral shaft fracture. This study aimed to examine the DASH-DLV with a more rigorous and extensive analysis by applying the Rasch model. Methods: Data of 400 patients included in a multicenter, prospective study comparing operative and nonoperative treatment of adult patients with a humeral shaft fracture were used. The person-item map, item fit statistics, reliability, response category ordering, and dimensionality were examined. Raw data were converted to linear measures using the Rasch model. Results: The DASH-DLV showed a good fit to the Rasch model, except for item 26 (“Tingling [pins and needles] in your arm, shoulder or hand”). The person reliability was 0.92. In general, the category functioning of the 5-point rating scale was working well. Dimensionality analysis revealed that the DASH-DLV is a unidimensional scale. Differential item functioning for sex was not detected, and only item 26 exhibited differential item functioning as a function for age. Conclusion: The DASH-DLV fits the stringent Rasch model in a clinical situation with a group of adult patients with a humeral shaft fracture. Adequate measurement for scientific research can be obtained to evaluate longitudinal intervention research.

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