Usability

Usability is the study of how people interact with manmade objects, both physical and electronic, in order to make it easier for the goal of the interaction to be achieved. In the computer field, usability falls under the heading of human-computer interaction. In engineering, it is considered part of industrial design.

Usability looks at items from the perspective of a person trying to use them and asks: Is the user able to do what they wanted to do with it? Was it easy to figure out how to use it? Could it be made easier? What was left out?

One of the biggest components of usability is accessibility, the adaptation of products to ensure they are usable by people with various disabilities: color blindness, motion impairments, low literacy, and so forth.

Principle of Least Astonishment

There is a principle of good human interface design, which goes back many years in computer science, often called "the principle of least astonishment." It is unclear who first coined the term.

Astonishment in activities of daily life

Before moving to the web, think of astonishment in daily life. While national conventions vary, a person entering a darkened room usually expects the light switch to be in a consistent place. Internationally, the conventions for using coin-operated telephones can vary greatly from country to country. Frequent business travelers, irritable from a long airplane flight, frequently mention the astonishment of trying to find the location of the headlight switch, and indeed the ignition key slot (and key release) in different models of automobile.

Delay in finding light switches, or in operating emergency equipment such as fire extinguishers, can have real safety consequences. Aviation safety improves when both cockpit crews, and ground controllers talking to pilots, use very standardized conventions for giving commands. In medicine, continuing attempts to reduce errors focus on avoiding giving drugs names that are close to those of others, and taking great precautions to avoid confusing injectable drugs with different concentration for different purposes.

Astonishment in telecommunications

While the principle is perhaps most often used with respect to the usability of World Wide Web pages, it appears in many other contexts. In telephony, whether traditional or voice over Internet Protocol, unpredictable pauses and variability in speech cadence, introduced by the communications system, are the greatest problems in understandability as measured by Mean Opinion Score and other metrics of user satisfaction.

Astonishment in basic computer interaction

Again going back long before the Web, another way computers annoy users in astonishment about interactive response time. Back in the days of mainframe computers, it was repeatedly found that users complaining about response time were more disturbed by similar actions taking wildly different amounts of time. A longer, but consistent, response time was far more acceptable.