The German Self-Efficacy for Rehabilitation Outcome Scale (SER-G) in patients undergoing primary total hip arthroplasty: a cross-cultural study into validity and reliability

Abstract Aim This study’s objectives are to (1) translate and culturally adapt the Self-Efficacy for Rehabilitation Outcome Scale into German (SER-G) and (2) examine its validity and reliability. Subject and methods One hundred sixteen German patients with hip osteoarthritis awaiting total hip arthroplasty (THA) completed the SER-G, Self-efficacy Expectations Scale (SES-G), Hip Disability and Osteoarthritis Outcome Scale (HOOS), and Hospital for Special Surgery Hip Expectation Survey (HSS-HRES) preoperatively. Structural validity was analyzed by explorative principal component (PCA) analysis with two predefined components. Construct validity was analyzed by formulating predefined hypotheses on relationships between the different questionnaires. Test–retest reliability was analyzed by assessing the SER-G a second time 2 weeks later. Reliability was assessed using Cronbach’s alpha, intraclass correlation coefficient (ICC 3,1), standard error of measurement (SEM), and minimal detectable change (MDC). The Bland–Altman plot was used to explore absolute agreement. Results The PCA confirmed two components explaining 74.8% of the variance. For construct validity, half of the predefined hypotheses were confirmed. Correlations with the other half of the hypotheses were lower than speculated, emphasizing the divergent validity of the SER-G. Internal consistency was good with a Cronbach alpha of 0.952; an ICC of 0.800 [0.705–0.864], together with a Bland–Altman plot, provided evidence of sufficient reliability. SEM was 0.80, MDC was 2.48 and 0.23 at the individual and group levels, respectively. Conclusion The SER-G can be considered a valid and reliable questionnaire to measure self-efficacy for rehabilitation after primary THA. Results were comparable to the previously established valid and reliable Swedish SER.