1. Research Design: Qualitative, Quantitative, and Mixed Methods Approaches, 4th Edition, by John W. Creswell.
2. Qualitative Research: A Guide to Design and Implementation 4th Edition, by Sharan B. Merriam (Author), Elizabeth J. Tisdell.
3. The Craft of Research, Third Edition, by Wayne C. Booth (Author), Gregory G. Colomb (Author), Joseph M. Williams.
4. The Research Methods Knowledge Base, 3rd Edition, by William M. K. Trochim (Author), James P. Donnelly.
5. Qualitative Inquiry and Research Design: Choosing Among Five Approaches 3rd Edition, by John W. Creswell.