Before we compare, let us understand the definitions of usability and accessibility for web.
Usability design is about designing products to be effective, efficient, and satisfying. The international standard, ISO 9241-11, provides guidance on usability and defines it 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”.
accessibility means that people with disabilities can perceive, understand, navigate, and interact with websites and applications, and that they can contribute equally without barriers.
Accessibility is a subset of usability. When a website or an application is made accessible, it means the product is useful for persons with disabilities. While satisfying the needs of users with disabilities in many instances all other users will also be benefited. Eg: Providing a clear link description that informs the target to the user is an accessibility requirement but greatly enhances the usability. Providing sufficient color contrast as per WCAG 2.0 standards is helpful for low vision users but greatly enhances the experience for mobile users in a day light.
Sometimes we find a problem on the page but find it difficult to judge if it is an accessibility problem or an usability problem or both or neither. Many accessibility consultants when finds a bug on the page that is definitely a problem for some set of disabilities but is not covered in a specific standard. They often go a step ahead and mark it as a best practice, good to have or an usability issue. Eg: Every focusable element on the page should have a visible focus indicator as per 2.4.7 focus visible. The visible focus indication depends on various factors such as the background of the element, browser tested on, use of additional styles for focus indicators or often the environment such as light focused on the screen. Raising it as an accessibility problem might be difficult but accessibility consultants will not be convinced to pass the scenario.
The below table compares Usability and accessibility on various parameters.
|ISO Standard||ISO/IEC 40500:2012||ISO9241|
|Users can||perceive, understand, navigate, and interact||effectively and efficiently use the design and are satisfied with it.|
|Caters the needs of||Every user but primarily the users with disabilities||All users|
|Overlap||Accessibility is a subset of usability||Usability is broader than accessibility|
|Quantifying||Measured accurately in most of the cases depending on number of instances the elements of the page fails to meet accessibility testing criteria.||Measuring depends on number of mistakes made by a user or the number of times they are frustrated or the time taken to complete a task.|
|Solutions||Most of the solutions to fix accessibility problems are technical and few are design centric.||Most of the solutions require design considerations and few are technical.|
|Testing process||An accessibility tester can individually test the website with the predefined set of testable statements and identify the problems.||Need to involve end users or create personas. Depending on the website, use cases need to be provided to the user. Usability analyst need to check the quantitative checks such as time taken to complete a task, errors made while completing etc. The qualitative analysis such as how easy to learn, Can the user remember the interface, the overall satisfaction etc need to be evaluated.|
Read the scenarios below to identify if a particular scenario falls under accessibility or usability or both accessibility and Usability.
- A shopping website is provided with same title in all pages. Is it an accessibility problem, usability problem or both usability and accessibility problem?
- A link text on the page has a color contrast ratio of 4.2: 1 with its background color but yet not clearly visible when observed in a day light. Is this an accessibility problem, usability problem or both usability and accessibility problem?
- A web page has pagination links. The clickable area of pagination links is too small for some users to accurately activate. Is it an accessibility problem or usability problem or both usability and accessibility problem?
- A registration form contains a password field that needs at least one number and one special character having a minimum of 8 characters long. No instruction is provided to inform the user about the same. Is it an accessibility problem or usability problem or both usability and accessibility problem?
- A difficult navigation mechanism on a website to send feedback on sites accessibility. Is it an accessibility problem or usability problem or both usability and accessibility problem?
- Usability and accessibility
- Usability and accessibility