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What is Usability?
January 9, 2013
It’s become increasingly obvious that user interfaces are important. How safe cars, trains, and cars are, and nuclear power plants for that matter, depends a great deal on how easy their interfaces are to use. If operators and drivers don’t understand key aspects of the interface, or if it becomes hard to use in stressful situations, then there is a big problem. Not surpringly then, there has been a big emphasis on making sure that user interfaces are easy to use. But just what is usability?
Usability is a broad concept that refers to how well a software interface or system fits the people who will be using it. If there is a good fit, then the interface or system tends to be easy to use. Usability is just one of a number of factors that determine the system. Other factors include cost, safety, reliability, maintainability, manufacturability, etc. However, poor usability can often be a show stopper, and usability is particularly important in highly engineered products where evolution and competition has led to satisfactory levels of the other evaluative criteria.
According to Jakob Nielsen (http://www.nngroup.com/articles/usability-101-introduction-to-usability/), usability consists of the following five attributes:
Learnability: Is the product easy to learn how to use?
Efficiency: Is the product efficient to use?
Errors: Do users make a lot of errors? Can they recover from them gracefully?
Satisfaction: Is the product satisfying to use?
Memorability: Can users easily remember how to perform tasks after they have been away from the system?
In his introduction to usability, Nielsen goes on to say:
“On the Web, usability is a necessary condition for survival. If a website is difficult to use, people leave. If thehomepage fails to clearly state what a company offers and what users can do on the site, people leave. If users get lost on a website, they leave. If a website’s information is hard to read or doesn’t answer users’ key questions, they leave. Note a pattern here? There’s no such thing as a user reading a website manual or otherwise spending much time trying to figure out an interface. There are plenty of other websites available; leaving is the first line of defense when users encounter a difficulty.”
There are many books on making interfaces more usable in general and a number of books on website usability. The book by Steve Krug is one of them. In keeping with its title, the book is short and according to its author is designed to be read by an executive on a two hour plane flight.
How does the topic of usability fit in with Human-Centred Systems Design?
Human Centred Systems Design is a broad topic that requires knowledge of human requirements, human capabilities, systems engineering principles, standards and documentation, and safety engineering, among a number of other topics.
At the core of human centred systems design is the need to fit the system to the user, rather than the other way around. Usability engineering is a set of evaluative methods that are built in to the design cycle so as to facilitate the usability of the resulting system. Usability engineering is not a single technique, but a collection of approaches that are still evolving.
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