Summary: In the early stages of a UX-design project, recruit enough people to gain an in-depth understanding of users’ experiences and needs. The number of people needed for an interview study is often smaller than you think.
One common question I get when teaching User Interviews , a full-day course at our UX Conference, is how many people do I need to interview ? Unfortunately, there isn’t a golden number. In this article, I’ll highlight some factors that will help you decide.
Some UX professionals assume that the recommendation to test with 5 users applies to interview-based studies as well. In fact, for many exploratory-research studies, 5 participants are too few . Others have been taught to recruit 5 people per persona , a rule of thumb to ensure that the sample is representative and large enough. However, this rule can result in many more interviews than necessary — especially when you have 5 or more personas. An experienced interviewer can extract in-depth insights from a much smaller number of interview sessions.
For quantitative research studies, it’s possible to perform sample-size calculations to tell us how many participants to recruit in order to confidently make generalizations to the wider population. But interviews are a qualitative research method. Qualitative research aims to understand the human experience in detail, not to determine how many people have had a given experience or express a particular need. (That’s what a follow-up quantitative study can tell us.) It’s not possible to know exactly how many participants is enough to gain this in-depth understanding.