Usability

Usability is a well-established concept in the theory and practice of human-computer interaction (HCI) design. HCI is concerned with the design, evaluation, and implementation of interactive computing systems for human use. Usability is particularly concerned with ensuring optimal relationships between humans and computers. Its goal is to develop computer systems that support rapid learning, high skill retention, and low error rates. Systems with high usability support high productivity, and are consistent, controllable, predictable, pleasant, and effective to use. Contemporary usability studies focus on World Wide Web usability, usability for online communities, and the creation of universal usability.

There is no concrete definition of usability, because usability encompasses multiple components that change over time as technology develops. However, it is generally agreed that there are five usability attributes:

• 1.
  Learnability. Systems should be easy to learn, so that users can quickly start working.
• 2.
  Efficiency. Systems should be efficient to use, so that users can quickly increase their productivity.
• 3.
  Memorability. Systems should be easy to remember, so that users can quickly reacquaint themselves with the system if time has elapsed since they last used the system.
• 4.
  Errors. Systems should have low error rates; if users do make errors, they should be quickly correctable.
• 5.
  Satisfaction. Systems should be pleasant to use, so that users are not reluctant to work on them.

Usability supports, rather than hinders, people's creativity. Three general principles help to ensure usability:

• 1.
  Consistency. Software should employ the same terms and procedures for achieving the same functionality throughout the program. Design elements (typography, color, font sizes, grammar, etc.) should be consistent.
• 2.
  Controllability. Let the users be in control of the software.
• 3.
  Predictability. Software that is consistent and controllable is predictable. Cross-platform stability is important.

Usability focuses on users—their tasks and their individual attributes, including physical and mental characteristics. It considers the users' experience with computer systems, and whether they are novice or expert users. Users are extraordinarily diverse, and parameters for discussing human diversity include physical, cognitive, perceptual, cultural, experience, age, gender, and capability elements.

Usability engineering refers to a set of activities that assesses human factors in involvement with computer systems. Ideally, usability engineering takes place throughout the life cycle of a product. Stages of the usability-engineering life cycle model include:

• 1.
  Developing the product and concept.
• 2.
  Knowing the user (cognizance of diverse user attributes, the relationship between the user and the job).
• 3.
  Setting usability goals.
• 4.
  Creating iterative design and refinements.
• 5.
  Providing rollout support.

Very often, usability testing involves participatory design: consulting with the actual users of a system in the design, development, and deployment of the technology. Participatory design processes are important, because they give users a voice in the design process, thus increasing the probability of a usable design; they enable both technical and non-technical participants to participate equally; and they provide opportunities for developers to meet, work with, and understand their users.

Ensuring universal usability for Web-based and other interactive information and communication technologies is a recent movement and call to action, spearheaded by many computer scientists, sociologists, and policymakers. Universal usability for the Web can be defined as having more than 90 percent of all households be successful users of information and communication services at least once a week.

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