When you go off with a doctoral research, the most difficult task, according to the masses is coming up with a topic but this is not the end of the story as another even difficult task waiting for you as soon as you finish your hunt for a topic is the research work you have to do with. The kind of research you need to do and the research methodologies you need to come up with depends upon the research subject and the angle with which you are covering the topic.
You can either use primary research i.e. doing you own research and collecting your very own live data but this must be started very soon in the process because most of the people are reluctant to participate in the interviews and the questionnaires are seldom filled with honesty. You can even go with secondary researches i.e. using someone else’s research and data and drawing your own fusion of results.
The research methodology is chosen to prove why you are doing things in a certain way and justify your points. You can use interviews or questionnaires or observational methods to deduce different levels of information. When going with one particular method keep notes for why you chose it, what other methods you could have chosen and the reason for dropping them?, Did you make any alterations in you research direction in order to keep with the chosen methodology? And when encountered dead ends, did you switch to some other methods?
Keeping track of all this information is vital to emerge successful from your dissertation defense.