1. Arthur K. B.(2008).Attachment styles and enneagram types: Development and testing of an integrated model for use in marriage and family therapy(Unpublished doctoral dissertation). Virginia Polytechnic Institute and State University Blacksburg VA.
2. The nature of love: Understanding the Enneagram types as nine expressions of attachment;Arthur K.;The Enneagram Journal,2010
3. Bartram D. &Brown A.(2005).Putting the person into personality: SHL Short research report 2005. SHL White paper.