Ary, D., Jacobs, L. C. & Sorensen, C: Introduction to Research in Education, 2010. Wadswoth, Australia. Chapter 20.
Bryman, A: Social research methods. 3rd ed, 2008. Oxford: Oxford University Press. Chapters 12, 20 - 22.
Leedy, P. D., Ormrod, J. E: research: Planning and design, 2013. Pearson: Boston. Chapters 2, 4, & 5.
Pallant, J: SPSS: Survival manual, 4th ed, 2010. McGraw-Hill, England. Chapters 3 – 12.
Patton, M. Q: Qualitative research & evaluation methods. Chapters 8 and 9 , 2002, 3rd. ed. . Sage publications.