Reliability and validity of the Swedish version of the Self-Efficacy for Rehabilitation outcome scale in persons with knee osteoarthritis

Abstract

Objective: To examine reliability and validity of the Swedish version of the Self-Efficacy for Rehabilitation (SER) outcome scale. Methods: One-hundred and ninety-eight inpatients (mean age 69 years) who underwent a primary total knee arthroplasty (TKA) due to knee osteoarthritis participated. They responded pre- and postoperatively to the SER outcome scale, and preoperatively to the Hospital Anxiety and Depression Scale (HAD) and the Knee Injury and Osteoarthritis Outcome Score (KOOS). Relative and absolute reliability were assessed. Internal consistency reliability was analysed with the Cronbach's alpha (α), and test–retest reliability with the intraclass correlation coefficient (ICC 2.1) and standard error of measurement (SEM%). Construct validity was analysed with explorative principal component analysis (PCA) and convergent validity with the Spearman's rang correlation test (rs). Results: For the SER outcome scale, the Cronbach's α was 0.97. The mean total score was 101.1 points on the 14th postoperative day and 101.4 points on the 21st postoperative day, with no systematic bias (p = 0.91) between the tests. The ICC was 0.78 and SEM% was 10%. The PCA explained 84% of total variance for two components. The correlation between SER and HAD was rs = − 0.23 (p = 0.002), and between SER and KOOS's five dimensions rs = − 0.02 to 0.15 (ns). Conclusion: The Swedish version of the SER outcome scale can be considered reliable and valid for assessing self-efficacy in patients with knee osteoarthritis. Increased self-efficacy may help the patients to choose appropriate coping strategies when performing physical activities after the operation.