Reliability, Validity, and Efficiency of an Item Response Theory-Based Balance Confidence Patient-Reported Outcome...

The aims of this study were to calibrate the original 16 items from the Activities-Specific Balance Confidence (ABC) Scale to create an item response theory (IRT)-based item bank and scoring metric of balance confidence (BC) and to assess psychometric properties of a computerized adaptive test (BC-CAT) and 6-item short-form (BC-SF) administration modes.

This retrospective study included data from patients who were treated in outpatient rehabilitation clinics and assessed for balance impairments by responding to the full ABC Scale at intake. IRT model assumptions of unidimensionality, local item independence, item fit, and presence of differential item functioning (DIF) were evaluated. BC-CAT-generated scores were assessed for reliability, validity, and administration efficiency, and the newly developed BC-SF was assessed for reliability.

Total cohort included 20,354 patients (mean age [SD] = 66 [16] years; range = 14-89). All 16 items were retained in the final item bank based on support for unidimensionality and fit to the IRT model. No items demonstrated DIF. Reliability estimates were 0.95, 0.96, and 0.98 for the BC-SF, BC-CAT, and the full item bank, respectively. Scores discriminated among patient groups in clinically logical ways. After controlling for scores at intake, better outcomes were achieved for patients who were younger, had more acute symptoms, exercised more, and had fewer comorbidities. Scores were responsive to change with a moderate effect size, with negligible floor and ceiling effects. CAT scores were generated using an average of 4.7 items (median = 4) and correlated highly with full-bank scores (Pearson correlation coefficient = 0.99).

The IRT-based BC patient-reported outcome measure (PROM) was reliable, valid, moderately responsive to change, and efficient, with excellent score coverage. The measure is suitable for research and routine clinical administration using the BC-CAT or BC-SF administration modes. The full ABC Scale can be administered for increased clinical content when appropriate.

The newly developed BC-PROM was reliable and valid for assessing perceived BC. In addition, the BC-PROM has efficient administration modes with low patient response burden, which enhances feasibility and promotes use during routine clinical practice in busy rehabilitation settings. This study supports a transition to PROMs that are based on modern measurement approaches to achieve the combined benefits of high accuracy and efficiency.