如果您想要单个号码，答案很简单：test 5 users in a usability study。Testing with 5 people lets you find almost as many usability problems as you'd find using many more test participants.
自从我开始推广以来，这个答案是一样的“折扣可用性工程“1989年。无论您是测试网站，内联网，PC应用程序还是移动应用程序都无关紧要。与5个用户，您几乎总是接近用户测试的最大效益 - 成本比。
- 定量研究(aiming at statistics, not insights): Test at least20.用户获得统计上的重要数量;紧密的置信区间需要更多的用户。
但是，这些例外不应该担心你：浩瀚majority of your user research should be qualitative- 即旨在收集insights to drive your design, not numbers to impress people in PowerPoint.
小测试的主要论点只是return on investment：testing costs increase with each additional study participant, yet the number of findings quickly reaches the point of diminishing returns. There's little additional benefit to running more than 5 people through the same study; ROI drops like a stone with a biggerN。
And if you have a big budget? Yay! Spend it on additional studies, not more users in each study.
Sadly, most companies insist on running bigger tests. During theUX Conference，我调查了217名参与者关于他们公司的做法。平均反应是他们使用的11考试参与者per round of user testing — more than twice the recommended size. Clearly, I need to better explain the benefits of small-N可用性测试。
"A big website has millions of users."样本大小并不重要,即使你我们re doing statistics. An opinion poll needs the same number of respondents to find out who will be elected mayor of Pittsburgh or president of France. The variance in statistical sampling is determined by the sample size, not the size of the full population from which the sample was drawn. In user testing, we focus on a website's functionality to see which design elements are easy or difficult to use. The evaluation of a design element's quality is independent of how many people use it. (Conversely, the decision about whether to fix a design flaw should certainly consider how much use it'll get: it might not be worth the effort to improve a feature that has few users; better to spend the effort recoding something with millions of users.)
"A big website has hundreds of features."这是运行几个的论据不同的测试- 每个关注较小的功能集 - 不是在每个测试中拥有更多用户。在贫穷的用户疲倦之前，您无法要求任何个人测试多少数任务。是的，您需要更多的用户，以实现丰富的功能，但您需要在许多研究中传播这些用户，每个研究都侧重于您的研究议程的子集。
- a medical site targeting both doctors and patients, and
When the users and their tasks are this different, you're essentially running a new test for each target audience, and you'll need close to 5 users per group. Typically, you can get away with 3–4 users per group because the user experience will overlap somewhat between the two groups. With, say, a financial site that targets novice, intermediate, and experienced investors, you might test 3 of each, for a total of 9 users — you won't need 15 users total to assess the site's usability.
"The site makes so much money that even the smallest usability problem is unacceptable."丰富的公司肯定有ROI case to spend more on usability。即使他们在每个质量改进上花费“太多”，而且由于流过用户界面的大量资金，他们将更加回复。然而，即使是最高价值的设计项目也将通过保持每项研究小并进行比较低价值项目的研究来优化他们的投资回报率。
The basic point is that it's okay to leave usability problems behind in any one version of the design as long as you're employing an迭代设计过程where you'll design and test additional versions. Anything not fixed now will be fixed next time. If you have many things to fix, simply plan for a lot of iterations. The end result will be higher quality (and thus higher business value) due to the additional iterations than from testing more users each time.
83 Case Studies
以下图表总结了Nielsen Norman Group最近的83个manbetx官方网站手机版usability consulting projects。每个DOT都是一个可用性研究，并显示了我们测试了多少用户以及我们向客户报告了多少用户发现。（图表仅包括正常的定性研究;我们还经常运行竞争性研究和基准测量，并在此显示其他类型的研究。）
- Finally, the very fact that these were consulting projects justified including a few more users, which is why we often run studies with around 8 users. ROI is the ratio between benefits and expense. When hiring a consultant, the true expense is higher than just the fee because the client must also spend time finding the consultant and negotiating the project. With higher investment, you want a larger benefit.
最后一点也解释了为什么真正的答案“有时候”有时可以小于5。如果你有一个敏捷-style UX process在非常低的开销中，您对每项研究的投资是如此普遍，即经济效益的比率通过较小的利益进行优化。（通过从每项研究中受益较少，似乎违反了投资回报，但出现了这种储蓄，因为每项研究的较小的开销让您跑得更多的研究，即许多小福利的总和变得大。）
真的low-overhead projects, it's often optimal to test as few as每项研究2个用户。对于其他一些项目，8个用户 - 或有时甚至更多 - 可能会更好。但是，对于大多数项目，您应该留下经过验证和真实的：5个用户每个可用性测试。