Number of participants for a test
Jakob Nielsen extensively analysed how many participants should be used to conduct a reliable usability study. The graphic below shows the connection between the percentage of usability problems found and the amount of participants.
The graphic shows that the amount of observed usability problems decreases from the sixth participant that is tested. With six participants (from the same target group) approximately 85 to 90% of the usability problem will be discovered.
In case of testing a more diverse, or a complex target group, or more than one target group, more participants should be tested. 2C holds to the basic principle that to conduct a usability test with multiple target groups, at least eight and a minimum of four participants for each target group should be tested.
The knowledge and experience of 2C’s usability experts results in discovering the remaining usability problems of the website. This is far more effective and inexpensive than testing with 12 or even 15 participants.
Usability testing is a way of doing qualitative research. This means it is less important that all participants experience a certain usability problem. When one user experiences a usability problem and this problem can be fixed, then fixing this problem should be considered.
