RASCH VALIDATION OF THE ACTIVITIES-SPECIFIC BALANCE CONFIDENCE SCALE AND ITS SHORT VERSIONS IN PATIENTS WITH PARKINSON'S DISEASE

Objective: To analyse in patients with Parkinson's disease the psychometric performance of the Activities-specific Balance Confidence scale (ABC) and its 3 short versions, using both a classical test theory approach and Rasch analysis. Methods: A sample of 217 patients with Parkinson's disease was assessed by ABC and the 3 short versions: Berg Balance Scale, Fear of Falling Measure, and the Unified Parkinson's Disease Rating Scale. Results: Cronbach's a was 0.95 in ABC, and ranged from 0.88 to 0.90 in its short versions. At Rasch analysis the 11 original rating categories were collapsed to 5 levels. In ABC 15 out of 16 items fitted the Rasch model. The ABC showed high correlation only with Fear of Falling Measure (r=0.85), and excellent correlation with its short versions (r>0.93). The 3 short versions showed a limited range of item difficulty estimates, low reliability levels, floor effect, a mismatch between mean item difficulty and mean ability of the patients. Conclusion: In patients with Parkinson's disease: (i) the ABC has an adequate unidimensionality; (ii) the selection of its items is satisfactory, although there is room for some minor refinement; (iii) the 0-10 rating scale should be simplified, and a 5-level response format seems able to improve the measurement qualities of the scale; (iv) the 3 short versions showed some psychometric limitations in comparison with the ABC.