Objective
To assess construct validity of the Prosthetic Limb Users Survey of Mobility (PLUS-M), a self-report mobility measure for people with lower limb amputation (LLA).
Design
Cross-sectional study.
Setting
Private prosthetic clinics (n=37).
Participants
Current lower limb prosthesis users (n=199, mean age=55.4±14.3 years, 71.4% male) were assessed before receiving a replacement prosthesis, prosthetic socket, and/or prosthetic knee.
Intervention
Not applicable.
Main Outcome Measure(s)
Convergent construct validity was examined using correlations between participants’ PLUS-M T-scores and measures of physical function, mobility, and balance, including the Amputee Mobility Predictor (AMP), Timed Up and Go (TUG), Patient Reported Outcomes Measurement Information System-Physical Function (PROMIS-PF), Prosthesis Evaluation Questionnaire-Mobility Subscale (PEQ-MS), and Activities-Specific Balance Confidence Scale (ABC). Known-groups construct validity was evaluated by comparing differences in PLUS-M T-scores among participants grouped by Medicare Functional Classification Level (MFCL).
Results
PLUS-M T-scores demonstrated a moderate positive relationship with AMP scores (rho=0.54, p<0.001) and a moderate negative relationship with TUG times (rho=- 0.56, p<0.001). The PLUS-M also showed a strong positive relationship with PEQ-MS scores (rho=0.78, p<0.001), ABC scores (rho=0.81, p<0.001), and PROMIS-PF T-scores (rho=0.81, p<0.001). Significant differences (p<0.05) in PLUS-M T-scores were found among groups of people classified by different MFCLs.
Conclusion
Study results support validity of the PLUS-M as a self-report measure of prosthetic mobility. Correlations between PLUS-M and measures of physical function, mobility, and balance indicate convergent construct validity. Similarly, significant differences in PLUS-M T-scores across MFCL groups provide evidence of known-groups construct validity. In summary, evidence indicates that PLUS-M has good construct validity among people with LLA.