When planning data collection for a qualitative research study, whether for a Ph.D. dissertation or a new business model, researchers often ask how many participants are enough? The answer is, enough is the amount where additional participants don’t provide any additional insights. We call this phenomenon “saturation.” You reach saturation when you are no longer learning very much (if anything) from each subsequent interview, observation, etc. So, how many do you “typically” need to reach saturation? Good question.
Minimum Sample Size
Guest, Bunce, and Johnson (2006) propose that saturation often occurs around 12 participants in homogeneous groups. This is consistent with my own experience during a recent CEO study where saturation occurred around 11 participants (Latham, 2013). To ensure that you have saturation you have to go beyond the point of saturation to make sure no new major concepts emerge in the next few interviews or observations. Consequently, 15 as a minimum for most qualitative interview studies works very well when the participants are homogeneous. Homogeneous means a particular “position” or level (e.g., top level executives) in the organization, a particular type of employee (e.g., customer service representatives), so on and so forth. For a particular group, saturation often occurs between 12 and 15. However, if you are interviewing different types of participants then you may need 12 to 15 of each type in order to reach saturation.
Enough is Enough
There is an old saying in research, “the more data points the better.” However, for practical reasons Crouch & McKenzie (2006) propose that less than 20 participants in a qualitative study helps a researcher build and maintain a close relationship and thus improve the “open” and “frank” exchange of information. This can help mitigate some of the bias and validity threats inherent in qualitative research. Consequently, the “sweet spot” sample size for many qualitative research studies is 15 to 20 homogeneous interview participants. Now, determining the number of cases to include in a multiple case study project is another issue and I will put forth a post on that in the next few weeks.
Use Peer Reviewed Pubs as Your Guide
While research methods textbooks are a good place to start, I recommend that you study the Guest, Bunce, and Johnson (2006) and Crouch & McKenzie (2006) papers as they provide much more detail on the considerations that you will want to include in your own sample size determination and subsequent justification.
- Crouch, M., & McKenzie, H. (2006). The logic of small samples in interview-based qualitative research. Social Science Information, 45(4), 18. doi: 10.1177/0539018406069584
- Guest, G., Bunce, A., & Johnson, L. (2006). How many interviews are enough? An experiment with data saturation and variability. Field Methods, 18(1), 24. doi: 10.1177/1525822X05279903
- Latham, J. R. (2013). A framework for leading the transformation to performance excellence part I: CEO perspectives on forces, facilitators, and strategic leadership systems. Quality Management Journal, 20(2), 22. | Download