1. Burns R. Burns R. (2009). Chapter 23: cluster analysis. In Business research methods and statistics using SPSS (pp. 552–567). California: Sage Publications.
2. Bryman A. (2012). Social research methods. Oxford: Oxford University Press.
3. Framing: Toward Clarification of a Fractured Paradigm
4. Flick U. (2009). An introduction to qualitative research (4th ed.). London: Sage Publications.