Several broad disciplines including Psychology, Human Factors and Cognitive Science subsume usability engineering, but the theoretical foundations of the field come from more specific domains: human perception and action; human cognition; behavioral research methodologies; and, to a lesser extent, quantitative and statistical analysis techniques.
When usability engineering began to emerge as a distinct area of professional practice in the mid- to late 1980s, many usability engineers had a background in Computer Science or in a sub-field of Psychology such as Perception, Cognition or Human Factors. Today, these academic areas still serve as springboards for the professional practitioner of usability engineering, but Cognitive Science departments and academic programs in Human-Computer Interaction now also produce their share of practitioners in the field.
Usability Engineers conduct usability evaluations of existing or proposed interfaces and their findings are fed back to the Designer for use in design or redesign. Common usability evaluation methods include usability testing, interviews, focus groups, questionnaires, cognitive walkthroughs, heuristic evaluations, cognitive task analysis and contextual inquiry. Of these, usability testing is generally held to be the gold standard of usability evaluation methods, though it is also one of the most involved and most expensive. Usability testing is when participants are recruited and asked to use the actual or prototype interface and their reactions, behaviors, errors, and self-reports in interviews are carefully observed and recorded by the Usability Engineer. On the basis of all this data, the Usability Engineer recommends interface changes to improve usability.
The term usability engineering (in contrast to interaction design and user experience design) implies more of a focus on assessing and making recommendations to improve usability than it does on design, though Usability Engineers may still engage in design to some extent, particularly design of wire-frames or other prototypes.
Usability engineers sometimes work to shape an interface such that it adheres to accepted operational definitions of user requirements. For example, the International Organisation for Standardisation-approved definitions (see e.g., IS0 9241 part 11) usability are held by some to be a context-dependent yardstick for the effectiveness, efficiency and satisfaction with which specific users should be able to perform tasks. Advocates of this approach engage in task analysis, then prototype interface design, and usability testing on those designs. On the basis of such tests, the technology is (ideally) re-designed or (occasionally) the operational targets for user performance are revised. [Dillon, 2000].