Revisiting the disabilities of the arm, shoulder and hand (DASH) and QuickDASH in rheumatoid arthritis
Background: Limitations in upper limb functioning are common in Musculoskeletal disorders and the Disabilities of
the Arm, Shoulder and Hand scale (DASH) has gained widespread use in this context. However, various concerns
have been raised about its construct validity and so this study seeks to examine this and other psychometric
aspects of both the DASH and QuickDASH from a modern test theory perspective.
Methods: Participants in the study were eligible if they had a confirmed diagnosis of Rheumatoid Arthritis (RA).
They were mailed a questionnaire booklet which included the DASH. Construct validity was examined by fit to the
Rasch measurement model. The degree of precision of both the DASH and QuickDASH were considered through
their Standard Error of Measurement (SEM).
Results: Three hundred and thirty-seven subjects with confirmed RA took part, with a mean age of 62.0 years
(SD12.1); 73.6% (n = 252) were female. The median standardized score on the DASH was 33 (IQR 17.5–55.0).
Significant misfit of the DASH and QuickDASH was observed but, after accommodating local dependency among
items in a two-testlet solution, satisfactory fit was obtained, supporting the unidimensionality of the total sets and
the sufficiency of the raw (ordinal or standardized) scores.
Conclusion: Having accommodated local response dependency in the DASH and QuickDASH item sets, their total
scores are shown to be valid, given they satisfy the Rasch model assumptions. The Rasch transformation should be
used whenever all items are used to calculate a change score, or to apply parametric statistics within an RA population.