What is Usability?

Usability is the ease of use of a system or a web site. It is a quality attribute that assesses how easy user interfaces are to use. If users either find a system difficult to use or find problems with it, then user adoption of this system is going to be extremely difficult.

Usability is a quality attribute that assesses how easy user interfaces are to use. The word "usability" also refers to methods for improving ease-of-use during the design process.

Usability is defined by 5 quality components:
  • Learnability: how easy is it for users to accomplish basic tasks the first time they encounter the design?
  • Efficiency: once users have learned the design, how quickly can they perform tasks?
  • Memorability: when users return to the design after a period of not using it, how easily can they reestablish proficiency?
  • Satisfaction: how pleasant is it to use the design?
There are many other important quality attributes. A key one is utility, which refers to the design's functionality: does it do what users need?
Usability and utility are equally important and together determine whether something is useful: It matters little that something is easy if it is not what you want. It is also no good if the system can hypothetically do what you want, but you can't make it happen because the user interface is too difficult. To study a design's utility, you can use the same user research methods that improve usability.
Definition: Utility = whether it provides the features you need.
Definition: Usability = how easy and pleasant these features are to use.
Definition: Useful = usability + utility.
Why Usability is Important?
On the web, usability is a necessary condition for survival. If a website is difficult to use, people leave. If the home page fails to clearly state what a company offers and what users can do on the site, people leave. If users get lost on a web site, they leave. If a web site's information is hard to read or doesn't answer users' key questions, they leave. Did you note a pattern here? There is no such thing as a user reading a web site manual or otherwise spending much time trying to figure out an interface. There are plenty of other web sites available, leaving is the first line of defense when users encounter a difficulty.
The first law of e-commerce is that if users cannot find the product, they cannot buy it either.
For intranets, content management systems, web portals usability is a matter of employee efficiency and productivity. Time users waste being lost on your intranet or pondering difficult instructions is money you waste by paying them to be at work without getting work done.
Current best practices call for spending about 10% of a design project's budget on usability. For internal design projects, think of doubling usability as cutting training budgets in half and doubling the number of transactions employees perform per hour. For external designs, think of doubling sales, doubling the number of registered users or customer leads, or doubling whatever other desired goal motivated your design project.
How to Improve Usability
There are many methods for studying usability, but the most basic and useful method is user testing, which has 3 components:
1. Get hold of some representative users, such as customers for a web site or employees for an intranet (in the latter case, they should work outside your department).
2. Ask the users to perform representative tasks with the design.
3. Observe what the users do, where they succeed, and where they have difficulties with the user interface. Do not talk and let the users do the talking.
It is important to test users individually and let them solve any problems on their own. If you help them or direct their attention to any particular part of the screen, you have contaminated the test results.
To identify a design's most important usability problems, testing 5 users is typically enough. Rather than run a big, expensive study, it is a better use of resources to run many small tests and revise the design between each one so you can fix the usability flaws as you identify them. Iterative design is the best way to increase the quality of user experience. The more versions and interface ideas you test with users, the better.
User testing is different from focus groups, which are a poor way of evaluating design usability. Focus groups have a place in market research, but to evaluate interaction designs you must closely observe individual users as they perform tasks with the user interface. Listening to what people say is misleading: you have to watch what they actually do.
When to Work on Usability
Usability plays a role in each stage of the design process. Therefore there is a need
for multiple studies.
Follow these steps: 
  • Before starting the new design, test the old design to identify the good parts that you should keep or emphasize, and the bad parts that give users trouble. Unless you are working on an intranet, test your competitors' designs to get data on a range of alternative interfaces that have similar features to your own.
  • Conduct a field study to see how users behave in their natural environment. Make paper prototypes of one or more new design ideas and test them. The less time you invest in these design ideas the better, because you will need to change them all based on the test results.
  • Refine the design ideas that test best through multiple iterations, gradually moving from low-fidelity prototyping to high-fidelity representations that run on the computer. Test each iteration.
  • Inspect the design relative to established usability guidelines, whether from your own earlier studies or published research.
  • Once you decide on and implement the final design, test it again. Subtle usability problems always creep in during implementation.
  • Don't defer user testing until you have a fully implemented design. If you do, it will be impossible to fix the vast majority of the critical usability problems that the test uncovers. Many of these problems are likely to be structural, and fixing them would require major re-architecting. 
The only way to a high-quality user experience is to start user testing early in the design process and to keep testing every step of the way.
Where to Test
It is best to test users in their own work environment, i.e. at their office. This will make them more comfortable. Also, users are used to their own computers. Be present with them while they use the design and just observe and make notes.
Misconceptions About Usability
Misconceptions about usability's expense, the time it involves, and its creative impact prevent companies from getting crucial user data, as does the erroneous belief that existing customer-feedback methods are a valid driver for interface design. Most companies still don't employ systematic usability methods to drive their design. The resulting widespread ignorance about usability has given rise to several misconceptions.
Misconception - Usability Is Expensive
Usual usability projects are not expensive. You can run user tests in a spare conference room or better yet in participants' offices. The methods are flexible and scale up or down according to circumstances. On average, best practices call for spending 10% of a design budget on usability. That is an inexpensive way to ensure that you spend the remaining 90% correctly, rather than blow your budget on an unworkable design.
Misconception - Usability Engineering Will Delay My Launch Date
Usability need not be on the grand scale. The simplest user testing method would take around 3 days but even faster tests are possible.
One of the main benefits of letting user research drive design is that you don't have to spend time on features that users don't need. Early studies will show you where to focus your resources so that you can launch on time.
Finally, usability can save time by helping you quickly settle arguments in the development team. Most projects waste countless staff hours as highly paid people sit in meetings and argue over what users might want or what they might do under various circumstances. Instead of debating, find out. It is faster, particularly because running a study requires only one team member's time.
Misconception - Usability Kills Creativity
Design is problem solving under constraints: you must design a system that can actually be built within budget and that works in the real world. Usability adds one more constraint: the system must be relatively easy for people to use. This constraint exists whether or not you include formal usability methods in your design process.
Human short-term memory holds only so many chunks of information. If you require users to remember too much, the design will be error-prone and hard to use because people will forget things when you overload their memory.
Also, if you are designing a web site, it will be one of millions available to users and they'll grant you only so much of their attention before they move on.
These are facts of life. All usability does is to make them explicit so that you can account for them in your design. Usability guidelines tell you how people typically behave with similar designs. User testing tells you how people behave with your proposed design. You can pay attention to this data or ignore it; the real world remains the same regardless.
Knowing real-world facts increases creativity because it offers designers ideas about design improvement and inspires them to focus their energy on real problems.
Misconception - We Don't Need Usability, We Already Listened to Customer Feedback
Market research methods such as focus groups and customer satisfaction surveys are great at researching your positioning or which messages to choose for an advertising campaign. They are not good at deciding user interface questions, in fact, they are often misleading.
When a group of people is sitting around a comfortable table having snacks, they are easily wowed by demos of a web site's fancy features and multimedia design elements. Get those people to sit alone at a computer, and they are likely to leave the same web site in a short time.
Seeing something demo'd and actually having to use it are two very different things.Likewise, what customers say and what customers do rarely line up; listening to customers uses the wrong method to collect the wrong data.
Luckily, the correct usability methods are inexpensive, easy to implement, and will not delay your project. Instead, relying on wrong methods or not doing usability work is much more expensive.
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