Research methods
Quantitative research methods (such as surveys) come with effective statistical techniques for determining a sample size. Big numbers.
Qualitative researchers need to set the context for stakeholders. These stakeholders tend to hear similar outcomes across research projects. Qualitative research methods such as interviews currently have no similar commonly accepted technique.
– Specific questions
– Fewer than 10 people. 5 is suggested by Jakob Nielson.
Interviews
Depth interviews allow you to speak to only a small number of people, but as the name suggests, you can gather some in-depth information. The idea is to get users to talk to you about their previous experiences when trying to complete goals relevant to your system. You need to talk to the theorized groups of users you initially de ned (for example, rst-time mother, mother of two or more, and somebody buying a gift for a mother). Discuss what they remember from the last time they completed their goal. In particular you want to know:
Some teams may have market research. Others may have customer service logs available. Maybe some web analytics. If not, even taken together, a design team might have a less-than-complete picture of how and why a design helps (or doesn’t help) real users in real situations reach their very real goals. How to resolve the conflicting opinions and fill in the gaps? Go watch your users use the design.
https://www.smashingmagazine.com/2017/03/user-research-sample-size-data/