Defining Usability
Usability determines how easy a design’s user interface is to use and how functional a product or design is. Key components of usability assess:
- How easy it is for users to learn the basic tasks of the interface;
- If users can perform those tasks quickly;
- If users can recall performing those tasks after time away from the interface;
- The number of errors, the severity of errors, and recovery from errors in the interface; and
- If the design satisfies users.
The effectiveness of the user interface, or fitness for purpose, and how much time goes into using the interface according to the user are evaluated during usability testing.
Definitions
There are a number of different definitions of usability.
The ISO definition of usability is:
“The extent to which a product can be used by specified users to achieve specified goals with effectiveness, efficiency, and satisfaction in a specified context of use.”
Whitney Quesenbery’s famous 5 E’s of usability.
According to this framework, a website with good usability should be:
- Effective, which means users can do what they want
- Efficient, which means they can do it quickly
- Easy to learn
- Error tolerant, which means that the site works to prevent errors or if someone makes an error, it helps them to fix the error and
- Engaging.
Steve Krug, definitions
Steve Krug has written some really great and highly accessible books about usability.
When he defines usability, he says:
It really just means making something that works well - that is - that a person of average or even below average ability and experience can use it for its intended purpose without getting hopelessly frustrated.
Steve Krug enhances this definition with his presentation of his first law of usability, which is don’t make me think.
This means that, as much as humanly possible, a website should be self-evident, obvious, and self-explanatory.
He writes that designing for usability means working to reduce the amount of thinking that people need to do when using your site by making things as self-evident as possible.
The more people have to stop and think about how to do what they want to do, where to click, where to find things, what things mean, whether something’s clickable, etc, the more that confidence in a site and user satisfaction are eroded.
What is a website usability issue?
- It’s anything that prevents task completion, slows the user down, takes the user off course, implies that things are okay when they’re not, or causes the user to misinterpret content.
- It’s anything that makes errors likely or difficult to recover from, or prevents the user from noticing something important, or from taking the next step.
- It’s anything that causes the user to look for a workaround or makes the user confused or irritated.
Usability vs User Experience
Usability is a sub-discipline under User Experience design. It’s an important element, but it isn’t the entire user experience. Key points of consideration for each area are:
Usability
- A design interface should be easy to use and allow users to become proficient.
- Users should be able to easily achieve their goals through the design.
- The interface should be easy to learn.
User Experience
- Usability: Users can arrive on a site, use it easily, and complete a given task.
- Useful content: A website should provide enough easily understandable information so that users can make informed decisions.
- Desirable/Pleasurable Content: The user forms an emotional bond with the product or website.
- Accessibility: A website should conform to accessibility standards to be accessible to users with disabilities.
- Credibility: How much trust a user feels for a website (including levels of security and privacy) plays a role in the user experience.
User-Centered Design
User-centered design puts the user at the center of every part of the design and development process. Taking this approach means:
- Involving users throughout the entire process, for example, through user research and user testing.
- Taking an iterative approach and conducting testing after each stage to ensure things are working well in reality.
- Conducting user testing for accessibility in the iterative cycles.
Commonalities
The components used for evaluating usability can also be applied to accessibility. Accessibility focuses on how usable and satisfying a product or service is to people with disabilities, including but not limited to people who use assistive technologies. In terms of usability, accessibility increases the chances of more people being able to use a product or design regardless of their abilities.
A Venn diagram consisting of two circles, one labeled usability and the other accessibility. The overlapping section shows the commonality between the two, that they focus on usability for everyone, including people with disabilities
More overlap occurs between usability and accessibility when accessibility practices increase usability for everyone and usability increases accessibility. Using high contrasting colors for web pages not only helps people who have low vision or colorblindness, but it also helps those using their devices in bright sunlight. Ensuring that a web page is keyboard accessible assists those who are blind, those who may have a motor disability, or users without disabilities who prefer to use keyboard strokes for browsing and navigating. Usability practices that promote using simple language and intuitive designs may assist those with cognitive disabilities to use a product or service more productively.
Differences
It is often difficult to tell the difference between usability and accessibility because there are indeed similarities between the two. There are times, though, when issues are just usability issues and when issues are truly accessibility issues.
Usability issues tend to affect every user, both users with disabilities and users without disabilities. All users face some difficulty using a product or service. Accessibility issues occur when people with disabilities encounter difficulties using or accessing a product or service.
There are also times when remediating accessibility issues may cause usability issues. For instance, if all images on a website are assigned very long text alternatives, the images may be accessible, but listening to long alternative text creates usability issues. There is a fine balance in ensuring that addressing accessibility issues does not cause usability issues and addressing usability issues does not create accessibility issues.
To help determine the differences between usability and accessibility in usability test reports, reports should highlight accessibility issues, detail which users with disabilities the issues affect, and state the specific accessibility standards the issues fail.