Revisiting the disabilities of the arm, shoulder and hand (DASH) and QuickDASH in rheumatoid arthritis

Abstract

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.