The Patient-Specific Functional Scale: Validity, Reliability, and Responsiveness in Patients With Upper Extremity Musculoskeletal Problems

Abstract

Clinical measurement, longitudinal; multicenter prospective cohort study. To examine the validity, reliability, and responsiveness of the Patient-Specific Functional Scale (PSFS) in patients with musculoskeletal upper extremity problems being treated in physical therapy. The clinimetric properties of the PSFS have not been established nor compared with region-specific outcome measures in patients with upper extremity problems. Patients completed the PSFS, Upper Extremity Functional Index (UEFI), and numeric pain rating scale (NPRS) at baseline and follow-up, and were categorized as improved, stable, or worsened, using the global rating of change. Construct validity was assessed by comparing the change scores of the stable and improved groups, using independent-samples t tests. Reliability was evaluated using intraclass correlation coefficient (ICC2,1) with 95% confidence intervals. Bland-Altman plots determined limits of agreement. Responsiveness and minimal important difference (MID) were determined with receiver operator characteristic (ROC) curves. One hundred eighty patients met the inclusion criteria. Construct validity was supported for the PSFS and the UEFI (P<.001). Reliability was moderate to good for the PSFS (ICC2,1 = 0.713) and UEFI (ICC2,1 = 0.848). Reported estimates of reliability may be lower than true values because the group of "stable" patients from this cohort had, on average, a small positive change. Bland-Altman plots indicated good agreement. The area under the ROC curve (AUC) was significantly different from the null value of 0.5 for the PSFS (0.887) and the UEFI (0.877), indicating good accuracy in distinguishing improved patients from stable patients. MID was 1.2 for the PSFS (scale, 0-10) and 8.5 for the UEFI (scale, 0-80). The PSFS is a valid, reliable, and responsive outcome measure for patients with upper extremity problems.