alculation with absolute agreement, and variability presented as 95% confidence interval, was used. Agreement was classified as follows: ICC ≤ 0.4 = poor; 0.4 to ≤0.8 = moderate; and ≥0.8 = good \[[@CIT0034]\].

Internal consistency was calculated with Cronbach's alpha to measure the degree to which single ESES-S items measured a common construct, and to assess the correlation between each item and the sum of the other items (corrected item-total correlation). For measuring common construct, alpha coefficients between 0.7 and 0.8 would be considered as minimally acceptable, 0.8--0.9 as respectable and over 0.9 as very good \[[@CIT0035]\]. For the corrected item-total correlation alpha coefficients over 0.4 are considered good \[[@CIT0038]\].

In order to assess validity of the ESES-S in an RA population, we formulated a number of hypotheses based on previous research on self-efficacy. For construct convergent validity, it was thus hypothesized that the ESES-S should correlate positively with HEPA, exercise \[[@CIT0039],[@CIT0040]\] and outcome expectations on physical activity \[[@CIT0040]\]. ESES-S should also correlate negatively with pain, activity limitation \[[@CIT0041],[@CIT0042]\] and fear avoidance beliefs \[[@CIT0043]\]. For construct divergent validity, the ESES-S should have no correlation with age or gender. To calculate validity, the Pearson correlation coefficient (*r*) was used and categorized as follows: 0.0--0.2 is a very weak relationship, 0.2--0.4 is weak, 0.4--0.6 is moderate, 0.6--0.8 is strong and 0.8--1.0 is very strong \[[@CIT0044]\]. Point-biserial correlation is a special case of the Pearson correlation coefficient, and was used to calculate the relation between dichotomized and interval variables \[[@CIT0045]\].

Ceiling and floor effects were examined for the ESES-S single items, as the percentage of individuals selecting the highest and lowest scores respectively. For the ESES-S total score, the percentage of individuals assigned to any of the 10 highest and 10 l