Identify 85% of Usability Problems with Only 5 Users

Lab Technician

You really don’t need an army of people to test your new design.

Just 5 people from your target audience will do.

Based on research from usability prophet Jakob Nielsen, the law of diminishing returns applies to usability testing.

In other words, more users equals more insights up to a point. That point, it turns out, is 5 people.

When you test 1 person you go from identifying 0% of the problems to identifying about 30%. The 2nd user identifies some of the same problems as the first user, along with a bunch of new ones. This pattern holds until you test your 5th person, at which point they identify more known problems than new ones and the effectiveness plummets.

So rather than test one design with 15 people, do 3 rounds of testing with 5 people each.

Then you can find most of your problems, fix them, and test for new problems in your optimized design twice. You’ll get much better results using an iterative approach than a blitz of 15 users all at once.

This method of optimization is people-centric and qualitative. You’ll observe user behavior and then act on it.

If you want quantitative and number-focused testing that focuses on your content rather than your users, a website conversion analysis would better suit you.