Qualitative usability studies have few users and variable protocol; numbers obtained from such studies are likely to poorly reflect the true behavior of your population due to large measurement errors.| Nielsen Norman Group
Qualitative research informs the design process; quantitative research provides a basis for benchmarking programs and ROI calculations.| Nielsen Norman Group
When collecting usability metrics, testing with 20 users typically offers a reasonably tight confidence interval.| Nielsen Norman Group
The answer is 5, except when it's not. Most arguments for using more test participants are wrong, but some tests should be bigger and some smaller.| Nielsen Norman Group
