It is important to distinguish between usability testing and usability engineering.
Usability testing is the measurement of ease of use of a product or piece of software.
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: Usability is often associated with the functionalities of the product (cf.
There is no consensus about the relation of the terms ergonomics (or human factors) and usability.
Some think of usability as the software specialization of the larger topic of ergonomics.
In software engineering, usability is the degree to which a software can be used by specified consumers to achieve quantified objectives with effectiveness, efficiency, and satisfaction in a quantified context of use.
The object of use can be a software application, website, book, tool, machine, process, vehicle, or anything a human interacts with.
According to Jakob Nielsen, "Studies of user behavior on the Web find a low tolerance for difficult designs or slow sites. And they don't want to learn how to use a home page.
There's no such thing as a training class or a manual for a Web site.
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.
Aiming for "intuitive" interfaces (based on reusing existing skills with interaction systems) could lead designers to discard a better design solution only because it would require a novel approach.
This position is sometimes illustrated with the remark that "The only intuitive interface is the nipple; everything else is learned." Instead, he advocates the term "intuitable," i.e., "that users could intuit the workings of an application by seeing it and using it." He continues, however, "But even that is a less than useful goal since only 25 percent of the population depends on intuition to perceive anything." ISO/TR 16902 ("Ergonomics of human-system interaction—Usability methods supporting human-centered design") is an International Standards Organization (ISO) standard that provides information on human-centered usability methods that can be used for design and evaluation.
For example, after observing and interviewing users, the usability expert may identify needed functionality or design flaws that were not anticipated.