Qualitative researchers care more about data saturation than sample size. This makes it difficult to estimate up front how many samples or participants will be necessary for a qualitative study.
Seaman and Yocco have each suggested that the number of users interviewed may vary depending on factors:
- the scope of the project, meaning the extent to which the results will be applied, will have the greatest bearing on the sample size; a familiar problem space will require fewer participants than an unfamiliar one
- the diversity of participants will increase the number you need to sample
- the experience of the researcher may reduce the required sample size
Seaman, Mitchel. “The Right Number of User Interviews.” Medium (blog), October 5, 2015. https://medium.com/@mitchelseaman/the-right-number-of-user-interviews-de11c7815d9.
Yocco, Victor. “Filling Up Your Tank, Or How To Justify User Research Sample Size And Data.” Smashing Magazine (blog). https://www.smashingmagazine.com/2017/03/user-research-sample-size-data/.