A very common question among master and PhD students doing qualitative research regards the number of the interviews that is considered to be “just enough” for doing qualitative research.
I think that Pratt (2009) answers this question perfectly!
“Unlike quantitative findings, qualitative findings lack an agreed-upon “significance level.” There is no “magic number” of interviews or observations that should be conducted in a qualitative research project. What is “enough” depends on what question a researcher seeks to answer. To illustrate, if a researchers wanted to study Supreme Court justices’ decision making, he or she would be limited to a very small sample. However, to examine how three cohorts of physicians changed their identities over the life of their residency programs, my colleagues and I had to conduct well over a 100 interviews (Pratt, Rockmann, & Kaufmann, 2006)” (Pratt, 2009: p. 856).
If you need a more elaborate and comprehensive answer you can check the paper of Baker and Edwards (2012) which is titled “How many qualitative interviews is enough”. The paper is based on responses from “14 renowned social scientists and 5 early career researchers”, who replied to the question “how many interviews is enough?”. Their responses call the attention on epistemological, methodological and practical issues that someone should take into consideration when conducting this kind of research. They give advices and tips about assessing research aims and objectives, validity within epistemic communities and available time and resources.
Hope I helped!
Baker, S.E. and Edwards, R. (2012) How many qualitative interviews is enough. Discussion Paper. (You can find it free here http://eprints.ncrm.ac.uk/2273/)
Pratt, M.G. (2009) From the Editors. For the lack of a boilerplate: Tips on writing up (and reviewing) qualitative research. Academy of Management Journal, 52(5): 856–862. (You can find it free here http://journals.aomonline.org/amj/editorials/Pratt_Oct%202009.PDF)