Measuring mobility in people with lower limb amputation: Rasch analysis of the mobility section of the prosthesis evaluation questionnaire

Objective: To assess the psychometric properties of the Mobility Section of the Prosthesis Evaluation Questionnaire (PEQ-MS). Design: A postal survey, including self-report assessment of prosthetic capability and performance with the PEQ-MS and the Locomotor Capabilities Index, and of other variables associated with prosthetic wear and use. The PEQ-MS data underwent Rasch analysis for rating scale diagnostics and a reliability and validity study. Patients: A total of 123 subjects (mean age 54 years) who had undergone lower limb amputation in the previous 5 years and who had completed rehabilitation and a prosthetic training programme. Results: According to Rasch analysis and expert review, some response categories of the PEQ-MS (13 items, 11-level numeric rating scale) were collapsed and one item was deleted. The remaining 12 items fitted to the Rasch model and created a revised scale with a 5-level response format, the PEQ-MS12/5. The PEQ-MS12/5 demonstrated good reliability (person-separation reliability = 0.95, item-separation reliability = 0.98) and internal construct validity. Moreover, the correlation with the Locomotor Capabilities Index (r(s) = 0.78) and with prosthetic wear and use (r(s) range 0.41-0.59) supported the convergent validity of the PEQ-MS 12/5. Conclusion: The new PEQ-MS12/5 presents good psychometric characteristics for measuring mobility in people with lower limb amputations. These preliminary results provide an already applicable instrument and a solid basis for further validation studies.