Clinical Interpretation of a Lower-Extremity Functional Scale–Derived Computerized Adaptive Test

Abstract

The increasing use of computerized adaptive tests (CATs) to generate outcome measures during rehabilitation has prompted questions concerning score interpretation. The purpose of this study was to describe meaningful interpretations of functional status (FS) outcome measures estimated with a body part-specific CAT developed from the Lower-Extremity Functional Scale (LEFS). This investigation was a prospective cohort study of 8,714 people who had hip impairments and were receiving physical therapy in 257 outpatient clinics in 31 states (United States) between January 2005 and June 2007. Four approaches were used to clinically interpret outcome data. First, the standard error of the estimate was used to construct the 90% confidence interval for each CAT-generated score estimate. Second, percentile ranks were applied to FS scores. Third, 2 threshold approaches were used to define individual subject-level change: statistically reliable change and clinically important change. The fourth approach was a functional staging method. The precision of a single score was estimated from the FS score +/-4. On the basis of the score distribution, 25th, 50th, and 75th percentile ranks corresponded to intake FS scores of 40, 48, and 59 and discharge FS scores of 50, 61, and 75, respectively. The reliable change index supported the conclusion that changes in FS scores of 7 or more units represented statistically reliable change, and receiver operating characteristic analyses supported the conclusion that changes in FS scores of 6 or more units represented minimal clinically important improvement. Participants were classified into 5 hierarchical levels of FS using a functional staging method. Because this study was a secondary analysis of prospectively collected data via a proprietary database management company, generalizability of results may be limited to participating clinics. The results demonstrated how outcome measures generated from the hip LEFS CAT can be interpreted to improve clinical meaning. This finding might facilitate the use of patient-reported outcomes by clinicians during rehabilitation services.