Students often wonder when they have enought data collected when doing qualitative research. The magic word is data saturation.
Data saturation is: ” .. New data tend to be redundant of data already collected. In interviews, when the researcher begins to hear the same comments again and again, data saturation is being reached… It is then time to stop collecting information and to start analysing what has been collected..” (Grady (1998: p. 26))
A more indepth explanation is provide in the article by Saunders et.al.(2017)
Saunders, B., Sim, J., Kingstone, T., Baker, S., Waterfield, J., Bartlam, B., … & Jinks, C. (2017). Saturation in qualitative research: exploring its conceptualization and operationalization. Quality & Quantity, 1-15.
Grady, M.P.(1998): Qualitative and Action Research: A Practitioner Handbook. Phi Delta Kappa Educational Foundation, Bloomington.