Rasch Analyses of the Activities-specific Balance Confidence Scale With Individuals 50 Years and Older With Lower-Limb Amputations

Sakakibara BM, Miller WC, Backman CL. Rasch analyses of the Activities-specific Balance Confidence Scale with individuals 50 years and older with lower-limb amputations. Arch Phys Med Rehabil 2011;92:1257-63. Objectives: To explore shortened response formats for use with the Activities-specific Balance Confidence (ABC) Scale and then evalute the unidimensionality of the scale, the item difficulty, the scale for redundancy and content gaps, and the item standard error of measurement (SEM) and internal consistency reliability among aging individuals with a lower-limb amputation living in the community. Design: Secondary analysis of cross-sectional survey and chart review data. Setting: Outpatient amputee clinics, Ontario, Canada. Participants: Community living adults (N=448; >= 50y; mean, 68y) who have used a prosthesis for at least 6 months for a major unilateral lower-limb amputation. Of the participants, 325 (72.5%) were men. Interventions: Not applicable. Main Outcome Measure: ABC Scale. Results: A 5-option response format outperformed 4- and 6-option formats. Factor analyses confirmed a unidimensional scale. The distance between response options is not the same for all items on the scale, evident by the Rasch Partial Credit Model (PCM) having a better fit to the data than the Rasch Rating Scale Model. Two items, however, did not fit the PCM within statistical reason. Revising the wording of the 2 items may resolve the misfit and improve the construct validity and lower the standard error of measurement. Overall, the difficulty of the scale's items is appropriate for use with aging individuals with lower-limb amputation, and is most reliable (Cron-bach alpha=0.94) for use with individuals with moderately low balance confidence levels. Conclusions: The ABC Scale with a simplified 5-option response format is a valid and reliable measure of balance confidence for use with individuals aging with a lower-limb amputation.