The structural validity of the Finnish version of the Disabilities of the Arm, Shoulder and Hand: A Rasch model analysis

Abstract

Introduction The construct validity of the Disabilities of the Arm, Shoulder and Hand questionnaire (DASH) has previously been questioned. The purpose of this study was to evaluate the measurement properties of the Finnish version of the DASH for assessing disability in patients with hand complaints using Rasch Measurement Theory. Methods A cohort of 193 patients with typical hand and wrist complaints were recruited at a surgery outpatient clinic. The DASH scores were analysed using the Rasch model for differential item functioning, unidimensionality, fit statistics, item residual correlation, coverage/targeting and reliability. Results In the original DASH questionnaire, the item response thresholds were disordered for 2 of 30 of the items. The item fit was poor for 9 of 30 of the items. Unidimensionality was not supported. There was substantial residual correlation between 87 pairs of items. Item reduction (chi square 95, degrees of freedom 50, p < 0.001) and constructing two testlets led to unidimensionality (chi square 0.64, degrees of freedom 4, p = 0.96). Person separation index was 0.95. The testlets had good fit with no differential item functioning towards age or gender. Conclusion Unidimensionality of the original Finnish version of the DASH was not supported, meaning the questionnaire seems to gauge traits other than disability alone. Hence, the clinician must be careful when trying to measure change in patients’ scores. Item reduction or the creation of testlets did not lead to good alternatives for the original Finnish DASH. Differential item functioning showed that the original Finnish scale exhibits minor response bias by age in one item. The original Finnish DASH covers different levels of ability well among typical hand surgery patients.

Structural validity of the Arabic version of the disabilities of the Arm, Shoulder and Hand (DASH) using Rasch measurement model

“…Consistent with our findings, DASH has been reported to violate the requirement of local item independence. A pattern of high residual correlation similar to ours where activity-related item group together while impairment-related items group together has been reported in patients with various upper extremity musculoskeletal disorders [ 15 , 16 , 18 , 34 , 36 , 37 ]. Similar to the approach used in the current study, Prodinger et al reported the use of two testlets (activity limitation and impairment testlets) to accommodate the issue of local dependency within the scale and this method yielded satisfactory fit to the Rasch model in line with the findings of the current study [ 34 ].…”

“…In patients with rheumatoid arthritis, Prodinger et al reported good fit of the same 2 testlets (activity limitation and impairment testlets) used in our study providing support to the findings of the current study [ 34 ]. Studies that examined the fit of the DASH to the Rasch measurement model reported a number of misfitting items ranging from 1 to 16 items [ 15 – 19 , 35 – 40 ]. All of the misfitting items in our study have been reported in the literature to deviate from the Rasch measurement model in different upper extremity musculoskeletal populations including patients with elbow disorders, shoulder disorders, hand disorders, Dupuytren’s contracture, humeral shaft fracture, and in patients with various upper extremity disorders [ 15 – 19 , 35 – 37 ].…”

“…Studies that examined the fit of the DASH to the Rasch measurement model reported a number of misfitting items ranging from 1 to 16 items [ 15 – 19 , 35 – 40 ]. All of the misfitting items in our study have been reported in the literature to deviate from the Rasch measurement model in different upper extremity musculoskeletal populations including patients with elbow disorders, shoulder disorders, hand disorders, Dupuytren’s contracture, humeral shaft fracture, and in patients with various upper extremity disorders [ 15 – 19 , 35 – 37 ]. Item 26 (tingling) was the most consistently reported misfitting item across these studies followed by item 30 (confidence).…”

“…All items with disordered thresholds in the Arabic DASH showed violation of local item independence as indicated by the high residual correlations. Prior studies that examined the internal structure of the DASH also pointed to disordered thresholds suggesting improper functioning of the scale response categories [ 15 – 18 , 35 , 37 – 39 ]. The number of items with disordered thresholds reported in the literature ranged from 2 items in patients with hand and elbow disorders [ 15 , 35 ] to 19 items in patients with various upper extremity disorders [ 18 ].…”

“…Similar to the findings of the current study, Prodinger et al reported that the DASH was sufficiently unidimensional in patients with rheumatoid arthritis after addressing the issue of local dependency between items using testlets [ 34 ]. The accommodation of local dependency through the use of testlets also led to unidimensionality of the Finnish DASH in patients with hand and wrist disorders[ 15 ]. Lack of unidimensionality of the DASH was reported in the literature in patients with hand disorders [ 16 ], Dupuyteren’s contracture [ 17 ], various upper extremity musculoskeletal disorders [ 18 , 19 ], shoulder disorders [ 36 ] and also in patient with stroke [ 40 ].…”