Rasch analysis of the Locomotor Capabilities Index-5 in people with lower limb amputation.

The aim of this study was to perform a Rasch analysis on the 5-level ordinal scale version of the Locomotor Capabilities Index (LCI-5), in order to investigate rating scale quality and conduct reliability and validity assessments. A questionnaire was mailed to 144 subjects who had undergone lower limb amputation (LLA) in the previous five years and completed a rehabilitation and prosthetic training programme. A total of 123 persons (85%) responded to the questionnaire, a self-report assessment of prosthetic capability and performance which included the LCI-5, the Mobility Section of the Prosthesis Evaluation Questionnaire (PEQ-MS) and other variables associated to prosthetic wear and use. Following Rasch analysis and expert review, the LCI-5 response categories level 1 ('yes, if someone helps me') and 2 ('yes, if someone is near me') were combined into a single category and 4 items were deleted (due to misfitting). The remaining 10 items fitted the Rasch model (LCI10-4) and demonstrated good reliability (person separation reliability = 0.94, item separation reliability = 0.98) and internal construct validity. Moreover, the good correlation with the PEQ-MS (r(s) = 0.77) and with prosthetic wear and use (r(s) range 0.34 - 0.51) supported the convergent validity of the scale. In conclusion, Rasch analysis provided the rationale for improving the measurement qualities of the LCI-5, refining its rating scale (through category diagnostics), identifying those items most useful for measuring the intended construct (as per the indexes of unidimensionality and internal construct validity) and showing that one can place high confidence in the consistency of both the person-ability and item-difficulty estimates obtained (reliability).