Self-management programs for patients with chronic illnesses, including rheumatic diseases, seek to enhance self-efficacy for performing health management behaviors. No measure of self-efficacy has been validated for patients with systemic sclerosis (SSc; scleroderma). The objective of this study was to assess the validity and internal consistency reliability of the Self-Efficacy for Managing Chronic Disease (SEMCD) scale in SSc.
English-speaking SSc patients enrolled in the Scleroderma Patient-centered Intervention Network Cohort who completed the SEMCD scale at their baseline assessment between March 2014 and June 2015 were included. Patients were enrolled from 21 sites in Canada, the US, and the UK. Confirmatory factor analysis (CFA) was used to evaluate the factor structure of the SEMCD scale. Cronbach's alpha was calculated to assess internal consistency reliability. Hypotheses on the direction and magnitude of Pearson's correlations with psychological and physical outcome measures were formulated and tested to examine convergent validity.
A total of 553 patients were included. CFA supported the single-factor structure of the SEMCD scale (Tucker Lewis Index = 0.99, comparative fit index = 0.99, root mean square error of approximation = 0.10). Internal consistency was high (α = 0.93), and correlations with measures of psychological and physical functioning were moderate to large (|r| = 0.48-0.67, P < 0.001), confirming study hypotheses.
Scores from the SEMCD scale are valid for measuring self-efficacy in patients with SSc, and results support using the scale as an outcome measure to evaluate the effectiveness of self-management programs in SSc.