Use the five usability objectives: learnability, efficiency, memorability, errors and satisfaction, as criteria for testing how successfully specified users complete defined tasks with a product. Gather evidence for each objective, compare the results with measurable benchmarks, and identify opportunities for improvement.
In user-centred design (UCD), usability depends on the user, task and context rather than on the product alone. Begin by selecting representative users and giving them a realistic task, such as asking first-time users to set a two-minute timer on a microwave.
| Usability objective | What to evaluate and measure |
|---|---|
| Learnability | How easily a first-time user reaches an acceptable level of competence. Measure time taken, requests for help or number of attempts. |
| Efficiency | How quickly and with how little effort a competent user completes the task. Measure completion time, number of actions or physical effort. |
| Memorability | How easily an occasional user operates the product after a period without using it. Repeat the test later and compare performance. |
| Errors | The number and seriousness of errors, including how easily users recognize and recover from them. Record error frequency, consequences and recovery time. |
| Satisfaction | How pleasant and acceptable users find the interaction. Collect ratings, interviews or questionnaire responses. |
For example, suppose eight users test the microwave. Six complete the task without help, the mean completion time is 25 seconds, three users make input errors, and average satisfaction is 3.5 out of 5. These results provide evidence that the controls may need clearer labels, better feedback or a simpler sequence.
A common misconception is that usability means only “easy to use.” Usability is multidimensional: a product may be quick to learn but inefficient during repeated use, or efficient but frustrating and error-prone.
