Nielsen Norman GroupEvidence-Based User Experience Research, Training, and Consulting
Watching users try to complete tasks with your interface is the most effective and productive way to uncover usability problems.
User testing can be done anywhere; witness our international studies, carried out with equipment that fit in a carry-on bag.
The answer is 5, except when it's not. Most arguments for using more test participants are wrong, but some tests should be bigger and some smaller.
3 approaches to better design: each has its uses, but the costs, benefits, and risks differ dramatically.
Simple usability tests where users think out loud are cheap, robust, flexible, and easy to learn. Thinking aloud should be the first tool in your UX toolbox, even though it entails some risks and doesn't solve all problems.
What is usability? How, when, and where to improve it? Why should you care? Overview answers basic questions + how to run fast user tests.