Justifying the methodology Your study is vulnerable to criticism if you don't adequately argue for your approach. What you do is often less important that how well you justify it. By paradigm I mean the overall approach. For example, I regards the family of experimental and quasi-experimental methods as one paradigm. Ethnographic approaches I regard as another.
Action research is a third.
As I use the term here, methodology is the particular sub-family used within a paradigm. These are the fine grain processes you use for data collection and the like. Focus groups constitute another. Document analysis is a third. For safe thesis writing, it is better to justify your choice of paradigm, methodology and methods.