It was written by a social psychologist that cites hundreds of credible sources. From this book I got basic definitions and the case study from Swan.
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Klassen, R. M., Krawchuk, L. L., & Rajani, S. (2008). Academic procrastination of undergraduates: Low self-efficacy to self-regulate predicts higher levels of procrastination. Contemporary Educational Psychology, 33, 915-931.
Robert Klassen is a professor of psychology at University of Alberta. He has contributed to many psychology publications, and is highly credible. He uses both qualitative and quantitative approaches to his research. This sourcr helped me link low self-esteem and procrastination in my paper.
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Kernis, Michael H. Psychological Inquiry, Vol. 14, No. 1 (2003), pp. 1-26 Published by: Taylor & Francis,