• M M P van der Heijden, F Pouwer, and V J M Pop.
• Department of Medical and Clinical Psychology, Center of Research on Psychology in Somatic Diseases (CoRPS), Tilburg University, P.O. Box: 90153, 5000, LE, Tilburg, The Netherlands, m.vdheijden@pozob.nl.
• Int J Behav Med. 2014 Apr 1; 21 (2): 394-401.

BackgroundExcercise self-efficacy is believed to influence physical activity bahavior.PurposeThe purpose of this study is to assess the psychometric aspects of the Exercise Self-efficacy Scale (ESS) in a type 2 diabetes Dutch Primary care sample.MethodType 2 diabetes patients (n = 322; <80 years old) filled in the ESS and the short questionnaire to assess health enhancing physical activity (SQUASH). The structural validity of the ESS was assessed by means of principal axis factor analyses and confirmatory factor analysis. In addition, reliability and concurrent validity with the SQUASH outcomes "total" and "leisure time minutes/week of moderate to vigorous intensity physical activity" were evaluated. T tests and ANOVAs were used to examine ESS scores in subgroups. In addition, a 13-item version of the ESS was developed.ResultsAnalyses were performed on complete cases (n = 255). Exploratory factor analysis suggested one underlying factor (total explained variance 54 %), with good internal consistency (α = 0.95). Confirmatory factor analysis showed a poor fit, as did a three-factor model suggested in an earlier research. Therefore, a 13-item ESS was developed with one underlying factor (total explained variance 59 %) and good internal consistency (α = 0.95). Both the 18-item and 13-item ESS correlated significantly with total and leisure time physical activity. ESS scores differed significantly between categories of education level and physical activity level.ConclusionThe 13-item ESS had sound psychometric properties in a large sample of primary care type 2 diabetes patients. The 13-item ESS could be useful in (intervention) research on physical activity in type 2 diabetes patients.

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