Data to which CDA is applied can vary - any textual source (e.g., books, policy, curriculum, etc.) or discursive form (e.g., speeches, debates, transcripts, narratives). CDA dictates what you look for, and how you look for it - and it must focus on issues of power (that's what the "critical" part of CDA addresses).
Readings to understand the method:
Fairclough, N. (1992). Discourse and Social Change. Cambridge: Polity Press.
van Dijk, T.A. (1993). Principles of critical discourse analysis. Discourse & Society, 4(2), 249-283.
Full text of Gee, J.P. (2011). How to do Discourse Analysis: A Toolkit. New York: Routledge.
A very handy, 20-step summary for doing critical discourse analysis based on Hill (2012).
Examples of its application in research:
Pinto, L.E. & Coulson, E. (2012). Social justice and the gender politics of financial literacy education. Canadian Journal of the Association for Curriculum Studies, 9(2), 54-85.
Bührmann, A.D., (2005). The Emerging of the Entrepreneurial Self and Its Current Hegemony. Some Basic Reflections on How to Analyze the Formation and Transformation of Modern Forms of Subjectivity. Forum: Qualitative Social Research, 6(1). Retrieved from: http://www.qualitative-research.net/index.php/fqs/article/view/518/1122
Additional notes:
Bührmann's (2005, see above for citation) study is an interesting CDA using a corpus of policy documents. She discusses "Variegated and interdependent levels of investigation" and these levels:- the object or area of knowledge
- the enunciative modalities
- the construction of concepts
- the strategic choice.
- power relations
- authority of authorization
- technologies of power
- strategies of power.