The Design Psychologist | Psychology for UX, Product, Service, Instructional, Interior, and Game Designers The Why Behind Sample Size: How Many People Do You Really Need to Test With?
Jun 30, 2025
How many participants do you really need for valid research? This discussion uncovers the often misunderstood world of sample sizes in user testing. From debunking the myth of testing just five users to understanding the power of participant numbers on design outcomes, insights abound. The psychological implications of too few versus just enough participants are explored, alongside methods to determine the optimal sample size based on your research goals. Gain clarity and confidence in your approach to user testing!
AI Snips
Chapters
Transcript
Episode notes
Skeptical Client on Sample Size
- Thomas Watkins shares a story about presenting research to a skeptical client questioning the sample size.
- The concern arose because only a couple dozen participants were included, sparking doubts about validity.
Effect Size Determines Sample Size
- Effect size impacts how many participants you need; bigger effects require fewer participants.
- Small effects blend into noise, so you need larger samples to detect them confidently.
Variability Increases Sample Needs
- Higher variability in your data means you need a larger sample size for stable estimates.
- Narrow variation allows confident conclusions with fewer participants.