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The article discusses the optimal number of users for usability testing in web design projects. The author argues that while some people believe that usability testing is expensive and time-consuming, it is actually more cost-effective to test with a small number of users multiple times rather than a single elaborate study with a large budget.The author presents a curve showing the relationship between the number of users tested and the insights gained. The curve indicates that each additional user adds less value to the insights gained, and beyond a certain point (around 5 users), the returns on investment decrease.The article recommends testing with at least 15 users to identify all usability problems in a design, but suggests that running multiple smaller tests with 3-5 users each is more effective because it distributes the budget more efficiently and allows for deeper insights into the design.The author also addresses the question of when to test with additional users, such as those from different groups or demographics. They recommend testing multiple groups of users with 3-4 users each, and 3 users from each group if testing three or more groups.Overall, the article emphasizes the importance of usability testing early and often in the design process to identify and fix problems before they become more serious issues down the line.