A study to measure how the website is easy for everyone to use, regardless of their special needs. It could be done by specific tools, following the W3C guideline or even by an usability test.
|Web Accessibility Evaluation Tools List||W3C|
|What is accessibility Testing?||Tutorials Point|
|Myth #5: Accessibility is expensive and difficult||UX Myths|
|Web Accessibility Testing||jimthatcher.com|