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Summary: Elaborate usability tests are a waste of resources. The best come from testing no more than 5 users and running as many small tests as you can afford. By Jakob Nielsen. Some people think that usability is very costly and complex and that user tests should be reserved for the rare web de project with a huge budget and a lavish time schedule. Not true. Elaborate usability tests are a waste of resources.
In earlier research, Tom Landauer and I showed that the of usability problems found in a usability test with n users is:. As soon as you collect data from a single test user , your insights shoot up and you have already learned almost a third of all there is to know about the usability of the de. The difference between zero and even a little bit of data is astounding. When you test the second user , you will discover that this person does some of the same things as the first user, so there is some overlap in what you learn.
People are definitely different, so there will also be something new that the second user does that you did not observe with the first user. So the second user adds some amount of new insight, but not nearly as much as the first user did. The third user will do many things that you already observed with the first user or with the second user and even some things that you have already seen twice. Plus, of course, the third user will generate a small amount of new data, even if not as much as the first and the second user did.
As you add more and more users, you learn less and less because you will keep seeing the same things again and again. There is no real need to keep observing the same thing multiple times, and you will be very motivated to go back to the drawing board and rede the site to eliminate the usability problems.
After the fifth user, you are wasting your time by observing the same findings repeatedly but not learning much new. The curve clearly shows that you need to test with at least 15 users to discover all the usability problems in the de. So why do I recommend testing with a much smaller of users? The main reason is that it is better to distribute your budget for user testing across many small tests instead of blowing everything on a single, elaborate study. Let us say that you do have the funding to recruit 15 representative customers and have them test your de.
Spend this budget on 3 studies with 5 users each! You want to run multiple tests because the real goal of usability engineering is to improve the de and not just to document its weaknesses. After creating the new de, you need to test again.
Even though I said that the rede should "fix" the problems found in the first study, the truth is that you think that the new de overcomes the problems. But since nobody can de the perfect user interface, there is no guarantee that the new de does in fact fix the problems. A second test will discover whether the fixes worked or whether they didn't. Also, in introducing a new de, there is always the risk of introducing a new usability problem, even if the old one did get fixed.
Finally, the second study will be able to probe deeper into the usability of the fundamental structure of the site, assessing issues like information architecture, task flow, and match with user needs. These important issues are often obscured in initial studies where the users are stumped by stupid surface-level usability problems that prevent them from really digging into the site.
So the second study will both serve as quality assurance of the outcome of the first study and help provide deeper insights as well. The second study will always lead to a new but smaller list of usability problems to fix in a rede. And the same insight applies to this rede: not all the fixes will work; some deeper issues will be uncovered after cleaning up the interface.
Thus, a third study is needed as well. The ultimate user experience is improved much more by 3 studies with 5 users each than by a single monster study with 15 users. You might think that 15 studies with a single user would be even better than 3 studies with 5 users. The curve does show that we learn much more from the first user than from any subsequent users, so why keep going?
Two reasons:. You need to test additional users when a website has several highly distinct groups of users. The formula only holds for comparable users who will be using the site in fairly similar ways. If, for example, you have a site that will be used by both children and parents, then the two groups of users will have sufficiently different behavior that it becomes necessary to test with people from both groups.
The same would be true for a system aimed at connecting purchasing agents with sales staff. Even when the groups of users are very different, there will still be great similarities between the observations from the two groups. All the users are human, after all. Also, many of the usability problems are related to the fundamental way people interact with the Web and the influence from other sites on user behavior.
In testing multiple groups of disparate users, you don't need to include as many members of each group as you would in a single test of a single group of users. The overlap between observations will ensure a better outcome from testing a smaller of people in each group. I recommend:. Nielsen, Jakob, and Landauer, Thomas K. Jakob Nielsen , Ph. Donald A. Norman former VP of research at Apple Computer.
Nielsen established the "discount usability engineering" movement for fast and cheap improvements of user interfaces and has invented several usability methods, including heuristic evaluation. He holds 79 United States patents, mainly on ways of making the Internet easier to use. The latest articles about interface usability, website de, and UX research from the Nielsen Norman Group. Subscribe to the weekly newsletter to get notified about future articles. Usability Testing with 5 Users: Information Foraging video 3 of 3. Share this article:.
Share this article: Twitter LinkedIn . About the Author Jakob Nielsen , Ph. Usability Testing with 5 Users: Information Foraging video 3 of 3 3 minute video.Recommended by 4 out of 5 people
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