Usability refers to the efficiency, comfort, safety and satisfaction with which a wide range of people and under a variety of conditions can perform their tasks with a product (i.e., a good or a service). It is much more than a measure of how easily a thing can be used, and it encompasses all aspects of the product and its use, including the hardware and software interfaces, the documentation, the packaging and even the services associated with the product. The meaning is similar to that of the term user-friendliness.
Usability is generally not something that can be merely added on as an afterthought during the final stages of product development or production. Rather, it usually must be considered from the very first stages of product planning and design and through final delivery and servicing. This is analogous to the concept of total quality control, which likewise must be taken into consideration from the very first stages of product planning, materials procurement, etc., in contrast to the common notion that quality control merely consists of testing completed products. It is also analogous to other aspects of product design, including security in computer software1.
Although it might seem, at least initially, that usability is an easy topic in comparison with other aspects of product development, experience shows that this is often not the case. And despite the fact that a number of guidelines have been established for maximizing usability, it remains as much an art as a science. This difficulty is evidenced by the fact that new or modified products are frequently introduced with poorly planned usability, which can reduce profitability or even cause the products to fail in a competitive environment.
In addition to the need to consider it at every stage of the product development cycle and for every aspect of a product's existence, another reason that maximizing usability can be so difficult is the existence of human variability, that is, the fact that there is a range of possible values for each of the numerous physical and mental characteristics of human beings. These differences among individuals, which include intelligence, education, experience, language, temperament, preferences, vision, handedness, disabilities and culture, must be considered if a product is to be appropriate for large numbers of people.
Usability is a very important consideration with regard to computers, and it is now ranked alongside such attributes as performance and robustness. Initially, computers were operated only by small numbers of highly trained specialists, and thus usability was of much less concern. In recent decades, however, they have come to be used by a vastly larger and more diverse group of people, most of whom have little professional training with regard to computers.
Computer usability can be subdivided into hardware and software aspects. The former includes such things as keyboards that are easy to use (e.g., the keys are not too small and the key stroke distances and bounce are appropriate) and screens that are pleasant and easy to see (e.g., realistic colors and minimal flicker and glare).
The usability of software is a vast and complex topic. This is in large part because individual programs can be extremely long and complex and because there are so many programs that must interact with each other. Another factor is that most software developers are specialists in programming rather than in usability.
Perhaps the most fundamental aspect in maximizing the usability of software is to make it intuitive so that people can utilize it with a minimum amount of training and frustration while not reducing any of its power or efficiency. Ideally, it should be designed so that it is rarely necessary for users to refer to separate documentation2, which, in turn, should also be written with maximum usability in mind. Specific examples of how software can be made more usable include not overloading the user with unnecessary information (sometimes referred to as the rule of silence), making web sites easy to navigate (i.e., to explore and find desired information), making it easy to avoid errors and to recover from them should they occur, making it easy to install new programs, and providing consistency of user interfaces.
Although usability is often thought of in terms of GUIs (graphical user interfaces) when discussing computer software, it actually applies just as much to command line (i.e., text-only mode) interfaces. UNIX, originally solely a command line operating system, was developed as a reaction to the excessively complex and non-intuitive operating systems that existed at that time, and its excellent usability was a major reason for its outstanding success (including that of its descendants more than 35 years later).
Accessibility is an integral part of usability. It is the ensuring that content can be easily accessed and read, viewed or heard by everyone, regardless of location, experience or the type of computer technology used. Content refers to material that is of interest to users, such as textual information, images, music and movies, and it generally excludes (1) formatting information, such as fonts, colors, positioning and borders, (2) software that is used to provide and render (i.e., convert to its final form) it and (3) unrelated advertising. Accessibility is most commonly discussed in relation to people with disabilities, because such people are likely to be the most disadvantaged if the principles of accessible design are not well implemented.
2This is in part because many computer users do not enjoy reading documentation and will thus try hard to avoid it. This aversion is largely a result of the fact that documentation is often poorly written and difficult to understand; that is, it lacks usability. Ideally, products should be designed so that they are self-documenting and that the user is not even aware that it is documentation; separate printed or on-line documentation should be readily available, but only for use as a last resort.
Created February 8, 2006.