Health Education Research Advance Access originally published online on October 11, 2006
Health Education Research 2006 21(Supplement 1):i33-i46; doi:10.1093/her/cyl106
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© 2006 The Author(s).
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Evaluating the properties of a stage-specific self-efficacy scale for physical activity using classical test theory, confirmatory factor analysis and item response modeling
1 Centre for Community Child Health Research, Department of Pediatrics, University of British Columbia, L408-4480 Oak Street, Vancouver, British Columbia V6H 3V4, Canada
2 School of Human Movement Studies, University of Queensland, Brisbane, Queensland 4972, Australia
3 Center for Health Promotion and Prevention Research, University of Texas Health Science Center at Houston, Houston, TX 77030, USA
4 Graduate School of Education, University of California Berkeley, Berkeley, CA 94720, USA
* Correspondence to: L. C. Mâsse. E-mail: lmasse{at}cw.bc.ca
The purpose of this paper was to evaluate the psychometric properties of a stage-specific self-efficacy scale for physical activity with classical test theory (CTT), confirmatory factor analysis (CFA) and item response modeling (IRM). Women who enrolled in the Women On The Move study completed a 20-item stage-specific self-efficacy scale developed for this study [n = 226, 51.1% African-American and 48.9% Hispanic women, mean age = 49.2 (±7.0) years, mean body mass index = 29.7 (±6.4)]. Three analyses were conducted: (i) a CTT item analysis, (ii) a CFA to validate the factor structure and (iii) an IRM analysis. The CTT item analysis and the CFA results showed that the scale had high internal consistency (ranging from 0.76 to 0.93) and a strong factor structure. Results also showed that the scale could be improved by modifying or eliminating some of the existing items without significantly altering the content of the scale. The IRM results also showed that the scale had few items that targeted high self-efficacy and the stage-specific assumption underlying the scale was rejected. In addition, the IRM analyses found that the five-point response format functioned more like a four-point response format. Overall, employing multiple methods to assess the psychometric properties of the stage-specific self-efficacy scale demonstrated the complimentary nature of these methods and it highlighted the strengths and weaknesses of this scale.
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