Qualitative research is less concerned with reaching a particular sample size. Its focus isn't on measuring scale, but on discovering high-level problems and mental models. Instead of sample size, qualitative researchers strive for data saturation: the point at which new data yields only minor, incremental returns and the broad trends have been identified. Therefore, as Seaman and Yocco have each argued, the number of users interviewed may vary depending on factors such as the diversity of your audience, the experience of the researcher, and the extent of the problem space.
In UX research, there is also often the advantage that the deliverable our research supports are rarely launched in their final form. As David Travis points out, working in an Agile environment, each product release is itself a research study and represents an opportunity to get further feedback that can help direct additional areas to focus research. Moreover, Travis argues, user researchers often purposely seek out edge cases who are more likely to surface potential problems.
Still, as Kay points out, researchers should take care the sample size is appropriate; it would be foolhardy, for instance, to use a small sample size for an A/B test. Moreover, user researchers should take care to not use the language of quantitative methods when describing qualitative results. For example, if we emphasize that five out of six users reported something, it may suggest a confidence interval that isn't wholly appropriate for a qualitative study.
- How many users should you interview
- Qualitative and quantitative research represent different philosophies of knowledge.
Kay, Joseph. “Why User Researchers Should Care about Sample Size.” Medium (blog), February 20, 2018. https://medium.com/designing-lyst/why-user-researchers-should-care-about-sample-size-fbb0b4215b3a.
Seaman, Mitchel. “The Right Number of User Interviews.” Medium (blog), October 5, 2015. https://medium.com/@mitchelseaman/the-right-number-of-user-interviews-de11c7815d9.
Travis, David. “Why You Don’t Need a Representative Sample in Your User Research.” Userfocus (blog). Accessed October 12, 2020. https://www.userfocus.co.uk/articles/myth-of-the-representative-sample.html.
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/.