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Test & Refine |
Learn About Evaluations
- How can you tell if your site is usable?
- What types of usability evaluations are there?
- When should you do usability evaluations?
- Which should you rely on more: usability evaluations or usability tests?
- What is a heuristic evaluation?
- How do usability tests differ from usability evaluations?
How can you tell if your site is usable?
To assess the usability of any product, including Web sites, you can use any or all of several methods. We divide these methods into two major types:
- Usability evaluations, which typically do not include users working with the product
- Usability tests, which focus on users working with the product
Our major focus at Usability.gov is on usability testing—having users work with the Web site to complete one or more tasks.
What types of usability evaluations are there?
"Usability evaluations" should not be confused with "usability tests." Evaluations require considerable judgment on the part of evaluators and usually do not include representative users.
Usability evaluations include:
- surveys and questionnaires
- observational evaluations
- guideline based reviews
- cognitive walkthroughs
- expert reviews
- heuristic evaluations
Learn more about Heuristic Evaluations.
When should you do usability evaluations?
You can do a usability evaluation as soon as you have a prototype to evaluate. Many usability professionals first do a usability evaluation and then follow it up with a usability test. They use the results of the evaluation to develop hypotheses about what could be serious problems and then develop the usability test around those hypotheses.
Which should you rely on more: usability evaluations or usability tests?
The results of a usability evaluation may or may not be consistent with the results of a usability test. In a usability evaluation, you are predicting the problems or successes that users will have with the Web site. A usability test with representative users tells you whether your predictions are valid.
What is a heuristic evaluation?
Probably the most popular evaluation method is referred to as a heuristic evaluation. In general, this is a method for finding usability issues in a user interface by having a small number of evaluators (usually one to five) examine the interface and judge its compliance with usability principles (heuristics). The resulting observations represent the evaluator's opinion about what needs to be improved in a user interface. Heuristic evaluations can be conducted on paper prototypes, PowerPoint wireframes, any other type of prototype, or fully functioning Web sites or Web applications.
When conducting a heuristic evaluation, each evaluator inspects the user interface and looks for problems. The most effective heuristic evaluations are conducted using several evaluators. When more than one person does a heuristic evaluation, it is best to have each evaluator do an independent evaluation and then combine their results.
Even good evaluators can miss usability issues, and all evaluators tend to believe that certain issues are problems when later testing shows that they are not. Several research studies have shown that about half of the usability issues identified by evaluators are not truly problems and that evaluators miss at least 25% of the real usability issues.
For a heuristic evaluation, it does not seem to matter much whether the evaluator inspects a low-fidelity prototype (for example, a PowerPoint wireframe) or a fully functional software prototype. About the same number of usability issues are detected in both cases.
Research shows that having expert usability specialists as evaluators is important and that the best evaluations are done by "double experts" who have both usability expertise and knowledge of the subject matter.
How do usability tests differ from usability evaluations?
Usability tests always including test participants; usability evaluations usually do not. Usability testing is the only way to know if the Web site actually has problems that keep people from having a successful and satisfying experience. (Of course, to have a useful usability test, the test participants must be representative of the people who use or will use the Web site.)
Generally, we are not interested in what testers think will be a problem; we want it demonstrated by having one or more users actually struggle with some aspect of the site. This is the true value of a usability test: It provides an opportunity for the site to allow users to succeed, succeed with difficulty, or totally fail. There is no guessing as to whether a scenario will be difficult to complete because participants (typical users) will succeed (or not), thus demonstrating that the Web site does or does not work for them.
Next steps
Now that you understand the difference between usability evaluations and usability testing, Learn About Usability Testing.
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