Usability engineering. Usability engineering is a professional discipline that focuses on improving the usability of interactive systems. It draws on theories from computer science and psychology to define problems that occur during the use of such a system. Usability Engineering involves the testing of designs at various stages of the development process, with users or with usability experts. The history of usability engineering in this context dates back to the 1980s. In 1988, authors John Whiteside and John Bennett—of Digital Equipment Corporation and IBM, respectively—published material on the subject, isolating the early setting of goals, iterative evaluation, and prototyping as key activities. The usability expert Jakob Nielsen is a leader in the field of usability engineering. In his 1993 book Usability Engineering, Nielsen describes methods to use throughout a product development process—so designers can ensure they take into account the most important barriers to learnability, efficiency, memorability, error-free use, and subjective satisfaction before implementing the product. Nielsen’s work describes how to perform usability tests and how to use usability heuristics in the usability engineering lifecycle. Ensuring good usability via this process prevents problems in product adoption after release. Rather than focusing on finding solutions for usability problems—which is the focus of a UX or interaction designer—a usability engineer mainly concentrates on the research phase. In this sense, it is not strictly a design role, and many usability engineers have a background in computer science because of this. Despite this point, its connection to the design trade is absolutely crucial, not least as it delivers the framework by which designers can work so as to be sure that their products will connect properly with their target usership.

International standards 

Usability engineers sometimes work to shape an interface such that it adheres to accepted operational definitions of user requirements documentation. For example, the International Organization for Standardization approved definitions (see e.g., ISO 9241 part 11) usability are held by some to be a context, 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 potentially redesigned if necessary.

The National Institute of Standards and Technology has collaborated with industry to develop the Common Industry Specification for Usability – Requirements, which serves as a guide for many industry professionals. The specifications for successful usability in biometrics were also developed by the NIST. Usability.gov, a no-longer maintained website formerly operated by the US General Services Administration, provided a tutorial and wide general reference for the design of usable websites.

Usability, especially with the goal of Universal Usability, encompasses the standards and guidelines of design for accessibility. The aim of these guidelines is to facilitate the use of a software application for people with disabilities. Some guidelines for web accessibility are:

The Web Accessibility Initiative Guidelines.
The Section 508 government guidelines applicable to all public-sector websites.
The ADA Guidelines for accessibility of state and local government websites.
The IBM Guidelines for accessibility of websites.

Errors 
In usability engineering, it's important target and identify human errors when interacting with the product of interest because if a user is expected to engage with a product, interface, or service in some way, the very introduction of a human in that engagement increases the potential of encountering human error. Error should be reduced as much as possible in order to avoid frustration or injury. There are two main types of human errors which are categorized as slips and mistakes. Slips are a very common kind of error involving automatic behaviors (i.e. typos, hitting the wrong menu item). When we experience slips, we have the correct goal in mind, but execute the wrong action.
Mistakes on the other hand involve conscious deliberation that result in the incorrect conclusion. When we experience mistakes, we have the wrong goal in mind and thereby execute the wrong action.

Even though slips are the more common type of error, they are no less dangerous. A certain type of slip error, a mode error, can be especially dangerous if a user is executing a high-risk task. For instance, if a user is operating a vehicle and does not realize they are in the wrong mode (i.e. reverse), they might step on the gas intending to drive, but instead accelerate into a garage wall or another car. In order to avoid modal errors, designers often employ modeless states in which users do not have to choose a mode at all, or they must execute a continuous action while intending to execute a certain mode (i.e. pressing a key continuously in order to activate "lasso" mode in Photoshop).

Evaluation methods 
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:
Card sorting
Cognitive task analysis
Cognitive walkthroughs
Contextual inquiry
Focus groups
Heuristic evaluations
Interviews
Questionnaires
RITE method
Surveys
Think aloud protocol
Usability testing

Software applications and development tools 
There are a variety of online resources that make the job of a usability engineer a little easier. Online tools are only a useful tool, and do not substitute for a complete usability engineering analysis. Some examples of these include:

The Web Metrics Tool Suite 
This is a product of the National Institute of Standards and Technology. This toolkit is focused on evaluating the HTML of a website versus a wide range of usability guidelines and includes:
 Web Static Analyzer Tool (WebSAT) – checks web page HTML against typical usability guidelines
 Web Category Analysis Tool (WebCAT) – lets the usability engineer construct and conduct a web category analysis
 Web Variable Instrumenter Program (WebVIP) – instruments a website to capture a log of user interaction
 Framework for Logging Usability Data (FLUD) – a file format and parser for representation of user interaction logs
 FLUDViz Tool – produces a 2D visualization of a single user session
 VisVIP Tool – produces a 3D visualization of user navigation paths through a website
 TreeDec – adds navigation aids to the pages of a website

The Usability Testing Environment (UTE) 
This tool is produced by Mind Design Systems is available freely to federal government employees. According to the official company website this tool consists of two tightly-integrated applications. The first is the UTE Manager, which helps a tester set up test scenarios (tasks) as well as survey and demographic questions. The UTE Manager also compiles the test results and produces customized reports and summary data, which can be used as quantitative measures of usability observations and recommendations.

The second UTE application is the UTE Runner. The UTE Runner presents the test participants with the test scenarios (tasks) as well as any demographic and survey questions. In addition, the UTE Runner tracks the actions of the subject throughout the test including clicks, keystrokes, and scrolling.

The UsableNet Liftmachine 
This tool is a product of UsableNet.com and implements the section 508 Usability and Accessibility guidelines as well as the W3C Web Accessibility Initiative Guidelines.

Notable practitioners 

 Deborah Mayhew
 Donald Norman
 Alan Cooper
 Jakob Nielsen
 John M. Carroll
 Larry Constantine 
 Mary Beth Rossen
 Steve Krug

Bibliography

External links 
Digital.gov

Usability.gov

The National Institute of Standards and Technology

The Web Accessibility Initiative Guidelines

References

Usability