The idea that usability and accessibility are interchangeable terms is a common misconception, according to Webcredible director Trenton Moss. Usability refers to “making the web site work for everyone”, and can be measured according to efficiency ­ how quickly users can complete tasks ­ satisfaction and overall experience, he said.
Usability can also be measured against the ISO13407 standard, although this is rather “woolly”, with little in the way of step-by-step guidance, said Moss. Although it depends greatly on the complexity of the web site, a complete overhaul to improve usability can take up to six months, according to Moss.
Accessibility, on the other hand, is about making the web site work for different user groups. Although it is often associated with the blind or visually impaired, the term relates to anyone who cannot physically access a site no matter what the cause, including technical reasons such as not being able to download ActiveX controls. Other groups who often find they are excluded from sites include the hard of hearing and those with reading or learning difficulties.
Accessibility is subject to more regulations than usability, with W3C Web Content Accessibility Guidelines forming the basic standard for many.