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Usability is the measure of how easily a thing can be used (typically a software application, website or a piece of hardware). This is generally defined in terms of the needs of the users of the thing. Often, designers' intentions directly conflict with these needs.

The term user friendly is often used as a synonym for usable, though it may also refer to accessibility. The use of terms user friendly and user friendliness should be avoided, as there are no widely accepted definitions for them, and they are thus often used as vague marketing terms.

Usability addresses the full spectrum of impacts upon user success and satisfaction. Usability can be accomplished through user-centered (not necessarily user-driven) design, although various techniques are employed (eg Psychological perspectives and software driven perspectives ). The usability designer provides a point-of-view that is not dependent upon computer programming goals because the usability designer's role is to act as the users' advocate. For example, after interacting with users, the usability designer may identify needed functionality or design flaws that were not anticipated.


Defining usability

ISO standard

The document ISO 9241-11 (1998) Guidance on Usability issued by International Standards Organization defines usability as:

The extent to which a product can be used by specified users to achieve specified goals with effectiveness, efficiency and satisfaction in a specified context of use.

Jakob Nielsen's framework of system acceptability

Usability consultant Jakob Nielsen has produces a framework of system acceptability, where usability is a part of usefulness and is composed of:

  • Learnability
  • Efficiency of use
  • Memorability
  • Few and noncatastrophic errors
  • Subjective satisfaction

Usability considerations

Usability includes considerations such as:

  • Who are the users, what do they know, and what can they learn?
  • What do users want or need to do?
  • What is the general background of the users?
  • What is the context in which the user is working?
  • What has to be left to the machine? What to the user?

Answers to these can be obtained by conducting user and task analysis at the start of the project.

Other considerations include:

  • Can users easily accomplish their intended tasks? For example, can users accomplished intended tasks at their intended speed?
  • How much training do users need?
  • What documentation or other supporting materials are available to help the user? Can users find the solutions they seek in these materials?
  • What and how many errors do users make when interacting with the product?
  • Can the user recover from errors? What do users have to do to recover from errors? Does the product help users recover from errors, for example, does software present informative, non-threatening error messages?
  • Are there provisions for meeting the special needs of users with disabilities? (accessibility)

Examples of ways to find answers to these and other questions are: user-focused requirements analysis, building user profiles, and usability testing.

Usability is now recognized as an important software quality attribute, earning its place among more traditional attributes such as performance and robustness. Indeed various academic programs focus on usability. [1] Also several usability consultancy companies have emerged, and traditional consultancy and design firms are offering similar services.

Usability professionals have their own Usability Professionals Organization [2].

Usability is the software specialization of the larger topic of human factors and ergonomics, although the term is also applied to document design.

See also


External links

Last updated: 05-07-2005 14:30:47
Last updated: 05-13-2005 07:56:04