Especially when using a grounded theory approach, seldom can this question be easily answered. In this research note, which reviews grounded theory studies that used interviewing as the primary data collection method, the author finds that typically 10 – 30 interviews are the normative range, although overall the range is from a low of 4 to more than 100 interviews.
The number of interviews depends on:
1) the research question: when the question is more focused fewer interviews are usually necessary
2) the researcher’s familiarity with the topic: increased knowledge may mean fewer interviews
3) single or multiple interviews: multiple interviews with a respondent may mean fewer interviews are necessary
But, at the end of the day, the primary decision factor is still theoretical saturation, which can only be assessed once data collection and analysis has begun.