Usability & Accessibility

In prior posts, I’ve described accessibility in many way. Accessibility boils down to giving equal services and independent access to people with disabilities. However, if a design process is led with universal design principles in mind, a website’s usefulness can go beyond WCAG success criteria and become usable by almost everyone. Usable websites create a design that:

  • provides an easy to use interface, whether intuitive or easy to learn, and
  • prioritizes functionality over design-for-the-sake-of-design.

Definitions of usability

ISO defines usability as 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 went further to break this definition down into the “5 E’s of Usability”:

  • effective
  • efficient
  • easy to learn
  • error tolerant
  • engaging

Steve Krug, author of Don’t Make Me Think said that usability is about:
“…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.” Krug also stated: “…a website should be self-evident, obvious, and self-explanatory.”

Key components of usability assessment are:

  • 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.


So, why am I learning about usability while I’m studying accessibility? Well, simply put:

accessibility increases usability for everyone, and usability increases accessibility for people with disabilities.

The key difference being that usability issues affect every user. As web designers and developers we can run across issues that may render a website or app unusable by everyone, but it shouldn’t be reported as an accessibility issue. Accessibility issues affect only people with disabilities, but, once corrected, may improve the usability of the site or app for everyone.

Additional reading