The WebAIM project (Web Accessibility in Mind) is a non-profit organisation which has, since 1999, provided web accessibility information, testing and training.
They are also well known for their WebAIM Million project where they analyse the homepages of 1 million popular websites to assess their accessibility. The 2023 version of this annual report found that the 1 million tested websites generated nearly 50 million accessibility errors across their homepages. This was an average of nearly 50 errors per homepage with a prevalence of 1 accessibility error for every 21 elements on a page.
Find out more about WebAIM and their work through the link in the Additional resources section.