Measuring activity limitations in walking: Development of a hierarchical scale for patients with lower-extremity disorders who live at home

Objective: To develop a hierarchical scale that measures activity limitations in walking in patients with lower-extremity disorders who live at home. Design: Cross-sectional study. Setting: Orthopedic workshops and outpatient clinics of secondary and tertiary care centers. Participants: Patients (N=981; mean +/- age standard deviation, 58.6 +/- 15.4y; 46% men) living at home, with different lower-extremity disorders: stroke, poliomyelitis, osteoarthritis, amputation, complex regional pain syndrome type 1, and diabetic and degenerative foot disorders. Interventions: Not applicable. Main Outcome Measures: (1) Fit of the monotone homogeneity model, indicating whether items can be used for measuring patients; (2) fit of the double monotorricity model, indicating invariant (hierarchical) item ordering; (3) intratest reliability, indicating repeatability of the sum score; (4) robustness, addressing the clinimetric properties within subgroups of patients; and (5) differential item functioning, addressing the validity of comparisons between subgroups of patients. Results: Thirty-five of 41 dichotomous items had (1) good fit of the monotone homogeneity model (coefficient H=.50), (2) good fit of the double monotorricity model (coefficient H-T=.33), (3) good intratest reliability (coefficient p=.95), (4) satisfactory robustness (within subgroups of patients defined by age, sex, and diagnosis), and (5) some differential item functioning (6 items in amputees compared with nonamputees). Conclusions: A hierarchical scale, with excellent scaling characteristics, was developed to measure activity limitations in walking in patients with lower-extremity disorders who live at home. The measurements should be interpreted cautiously when making comparisons between amputees and nonamputees.