Improving the action research arm test: a unidimensional hierarchical scale. Clin. Rehabil. 16, 646–653. doi: 10.1191/0269215502 cr534oa

Background: The Action Research Arm (ARA) test is a performance test of upper extremity motor function which consists of 19 items divided into four hierarchical subtests. This multidimensionality has not yet been tested empirically. Objective: To investigate the dimensionality of the ARA test. Design: Cross-sectional study involving a sample of 63 chronic stroke patients. Methods: A Mokken scale analysis was performed. Results: The Mokken scale analysis revealed one strong unidimensional scale containing all 19 items, of which the scalability coefcient H was 0.79, while H per item ranged from 0.69 to 0.86. The reliability coefcient rho equalled 0.98, indicating a very high internal consistency. A subset of 15 out of 19 items showed an invariant hierarchical item-ordering. Conclusion: The ARA test is a unidimensional scale. The use of subtests, as proposed in the original description of the instrument, is not supported by th