This article is about the human-computer interaction concept. For the User Friendly webcomics, see User Friendly.

Usability is the measure of the ease with which particular people can employ a particular tool or other human-made object in order to achieve a particular goal. Usability can also refer to the methods of measuring usability and the study of the principles that may predict whether an object is found usable in practice.

In human-computer interaction and computer science, usability usually refers to the usability of the user interface of a computer program or a web site. The term is also used often in the context of consumer electronics (such as a remote control or a car stereo), somewhat often in the context of communication, and knowledge transfer objects (such as a cookbook, a document or online help), and sometimes in the context of mechanical objects (such as a door handle or a hammer).



The primary notion of usability is that objects which are designed with their users' psychology and physiology in mind are, for example:

  • more efficient to use — it takes less time to accomplish a particular task
  • easier to learn — operation can be learned by observing the object
  • more satisfying to use

Complex computer systems are finding their way into everyday life, and at the same time the market is becoming saturated with competing brands. This has lead to usability becoming more popular and widely recognised in recent years as companies see the benefits of researching and developing their products with user-oriented instead of technology-oriented methods. By understanding and researching the interaction between product and it's users, the usability expert can also provide insight that is unattainable by traditional company-oriented market research. For example, after observing and interviewing users, the usability expert may identify needed functionality or design flaws that were not anticipated.

In the user-centered design paradigm, the product is designed with its intended users in mind at all times. In the user-driven or participatory design paradigm, some of the users become actual or de facto members of the design team.

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 without much substance.

There is no consensus about the relation of the terms ergonomics (or human factors) and usability. Some think usability as the software specialization of the larger topic of ergonomics. Others view these topics as tangential, with ergonomics focusing on physiological matters (i.e. turning a door handle) and usability focusing on psychological matters (i.e. recognising that this door can be opened by turning that handle).

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 and computer science professor Ben Shneiderman have written (separately) about 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 accomplish 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.

See also


External links

es:Usabilidad fi:Kytettvyys it:User friendly nl:Gebruiksvriendelijkheid ja:ユーザビリティ sv:Anvndarvnlig zh:可用性


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