1. Denzin NK, Lincoln Y. The sage handbook of qualitative research. Thousand Oaks: Sage; 2005.
2. Ritchie J, Lewis J. Qualitative research practice. A guide for social science students and researchers. London: Sage Publications; 2007.
3. Strauss AL, Corbin JM. Basics of qualitative research: techniques and procedures for developing grounded theory. 2nd ed. Thousand Oaks: Sage Publications; 1998.
4. Bowling A. Research methods in health. England: Investigating health and health services; 2002.
5. Sarantakos S: Social Research: Palgrave Macmillan: Hampshire; 2005.