Objective: To validate the unidimensionality of the Action Research Arm Test (ARAT) by
Mokken scale analysis and to examine whether the ordinal raw sum scores of ARAT can be
transformed to interval scores via the Rasch rating scale model.
Subjects and Methods: A total of 351 patients were recruited from five rehabilitation
departments located in four regions of Taiwan. The 19-item ARAT was administered to all the
subjects by a physical therapist. The data were analyzed by Mokken analysis, followed by
Results: The results strongly supported a unidimensional scale of the 19-item ARAT by
Mokken analysis, with the scalability coefficient H = 0.95. Except for the item “pinch ball
bearing 3rd finger and thumb”, the remaining 18 ARAT items form a constant hierarchical
scale for all stroke patients. On the other hand, the Rasch analysis, with a stepwise deletion of
misfit items, showed that only 4 items (“grasp ball”, “grasp block 5 cm3”, “grasp block 2.5
cm3”, and “grip tube 1 cm”) fit the rating scale model's expectation.
Conclusions: Our results provided strong evidence that the ARAT forms a unidimensional
scale for patients with stroke. However, the results did not support the premise that the ordinal
total raw sum scores of the ARAT can be transformed into interval Rasch scores. Thus,
patients can be ranked on their upper extremity functional abilities by the raw sum scores, but
equal differences in these scores do not imply equal differences in functional status. The score
changes within patients and the score differences between patients can only give us the
information about order of the patients, but not represent exact function of them.
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