Usability Testing: Why 5 Users Are Enough

Nielsen reports that testing with just 5 users per iterative cycle will give you the best results (1). His research shows that testing with just 1 user will uncover close to 1/3 of the most obvious usability problems. This drives home the point that any testing is better than no testing.

Testing with 3 users in your first cycle will uncover 85% of the most obvious usability problems. After the first 3 users, the number of usability issues uncovered with each following user tested with is small.

The usability problems uncovered will be those that are most obvious. They will be the ones that are most often encountered by your users.

Testing 5 Users Means More Iterations

Nielsen recommends conducting tests in multiple iterations. You should aim for testing with 15 users in 3 design cycles. Remember, the goal of usability testing is to improve your designs, not just report the problems. Iterative testing lets you do that.

After your first cycle of testing, redesign the product with fixes to the usability problems. Next, run another cycle of testing with 5 more users. This testing is essential to make sure that design changes made fix the problems with the first design. Remember, you are not your user so you have to test with real users. Also keep in mind that your new design may have created usability problems of their own. Therefore you need to test to make sure that no new ones have been created.

The 2nd and 3rd iterations also give you the chance to go deeper into the structure of your website or app. In the first cycle, users tend to stumble on surface-level usability problems. This means they may fail to encounter deeper lying problems. In subsequent usability testing cycles you get a chance to get to these issues.

When 5 Users Isn’t The Right Number

In some cases, testing with 5 users will not be enough. Websites may have more than one type of user group. For these sites, there may be significant differences in the goals and motivations for using your site of each group. In such instances, you may need to run tests with 15 users from each of the different user groups.

Testing with 15 users in 3 cycles will not guarantee uncovering problems that affect only a few of your users. In these situations, we recommend combining usability testing with expert reviews.

Summary

  • Research shows that testing with just 5 users per cycle will give you the best results
  • Testing with 3 users in a single cycle will uncover 85% of the most obvious usability problems
  • The goal of usability testing is to improve the design, not just to report the problems, that’s why testing should be iterative
  • The ideal number of users to test with is 15 in 3 cycles, i.e. 5 per cycle
  • In certain scenarios, 5 users per cycle may not be enough

Learn From the UXBERTS

At UXBERT we offer hands-on training in each step of the user-centered design process. In our Usability Testing & Expert Reviews workshop, we will teach you all the basic tools and techniques you need to carry out effective usability testing on your product. We keep our class sizes small to deliver a complete learning experience so we have limited seats available. Don’t miss out, buy your ticket now through this link!

 

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