Which is greater?
Usability > Accessibility OR Accessibility > Usability
I have read and heard many viewpoints on this for many years. The majority seem to favor the idea that accessibility is a subset of usability — which seems to posit that a digital product must first be usable and then can be (or made to be) accessible once so. However, it can also suggest that it is a criterion of usability and that in order to be usable, it must be accessible. This is the proverbial chicken and egg scenario. Or is it a Matryoshka doll scenario?
In order to examine this and conclude which comes first, one must first define these terms.
Usability is a grading factor on the ease of use — specifically toward task completion or a goal. As the ISO defines, a specified user for a specified goal. A digital product or software is either more or less usable based on measuring against criteria — most of which are objective and quantitative, some of which are subjective and qualitative, and some vary by type and context — for effectiveness, efficiency and satisfaction. The criteria or principles often include at least:
- Clear. Requires minimal effort to learn and understand.
- Discoverable. Everything required can be easily found.
- Zero barriers. There should be no obstacles or friction. Errors should be preventable and easily recoverable.
- Efficient. Tasks should be able to be completed as expected, with as few steps and as quickly as possible.
Essentially, it answers not just “can this be used?”, but “how well?”
Accessibility deals more in who. This is unfortunately often defined as an accommodation for people with disabilities. The intent is not to accommodate any specific group, disability, impairment, condition or context, but to inclusively design digital products in such a way that all people benefit in all cases. In other words, accessibility is a measure against criteria and principles that are known and widely accepted to ensure (barrier-free) access to a digital product by all people — regardless of ability. These are collectively known as the Web Content Accessibility Guidelines (WCAG). The essential principles are: perceivable, operable, understandable and robust. Each of these then have individual criteria. It is possible to pass all relevant success criteria and still be a challenge for someone to access. So then, it fails the “all people” intent. A recent conversation on this resulted in a post (link below) on the fact that accessible > WCAG.
Usability is an ease-of-use factor. Accessibility is an everyone-can-use factor.
If a website is easy to use for some people, but not all people, it is not accessible — and arguably, not truly usable. If instead, it is accessible to all people, but difficult to locate content or inefficient, then it is still not very usable. So it is possible to be:
- usable for some but not accessible
- accessible for all but not usable
- both usable and accessible
- neither usable nor accessible
In discussing the ‘distinctions and overlap’, the W3C Web Accessibility Initiative (WAI) states “In practice, basic accessibility is a prerequisite for usability.”
So, are they equal? Are they at odds or share an inverse ratio? Are they additive? Are they a Venn diagram with a wide intersection? Or facets on Morville’s UX Honeycomb? Is one greater than the other? Is one a sub-discipline of the other? Does it matter?
Clearly they are both important.
Let’s examine an order of operations. Can I accurately measure the effectiveness, efficiency and satisfaction if I cannot perceive or understand it? Perhaps, but clearly the result is poor. Can I accurately measure if it is perceivable, operable, understandable and robust if there are barriers to access and discovery? Most likely not.
So here is the simple truth. Usability can only be a measure of use. If it cannot be accessed, it cannot be used. A website or digital product must first be accessible, and then usable. When it is accessible, it is inherently usable by all. Then, the degree of how well can be measured for all. Enhancing accessibility means that more people can engage with it in a meaningful way. Enhancing usability means that those people will be more effective with less effort and higher satisfaction.
Accessibility > Usability