Assessment of capacity for myoelectric control: evaluation of construct and rating scale.

OBJECTIVE To examine the construct and rating scale of the Assessment of Capacity for Myoelectric Control, an assessment to evaluate ability in using a prosthetic hand. DESIGN Cross-sectional study. SUBJECTS Upper limb prosthesis users with different prosthetic levels/sides and prosthetic experience were included (n = 96). METHODS Subjects' assessments with the Assessment of Capacity for Myoelectric Control were collected by 6 raters during their regular hospital visits. Rasch analysis was used, since it allowed an analysis of the data at the item and category levels. Dimension, item hierarchy and item fit statistics were used to examine the construct. Different Rasch parameters were used to examine rating scale structure and its use. RESULTS The consistency of item difficulties with clinical knowledge and the unidimensionality confirmed that the construct is valid. Two items functioned unexpectedly (misfit), but the misfit was idiosyncratic to the sample, not systematic to the items. The 4-point rating scale usefully differentiated the subjects on the basis of their abilities. The use of category 2 was somewhat redundant. CONCLUSION The Assessment of Capacity for Myoelectric Control is a valid assessment that evaluates ability in using a prosthetic hand. Revision of the category 2 definition would improve the functioning of the rating scale.