Re: accessibility and usability

"Barbara de Zoete" <b_de_zoete (AT) hotmail (DOT) com> writes:

[F'up set to ciwas-d]

I am getting more and more confused as to the meaning of the words
'accessibility' and 'usability' *in the context of the world wide web*.
What do these two words mean? How do they differ from one another?
Where does the meaning overlap, if it does? Where do they perhaps
conflict with one another, if they do?

Can anyone please explain to someone who is not native speaking, nor
fluent in English?

As a rough guideline:

Accessibility improvements significantly increase the ease of access
to content (or make it possible at all) for a subset of users [1].

Usability improvements increase the ease of access to content for most
or all users to a similar degree.

Obviously there's a lot of overlap.

Alternatively:

Accessibility can be divided into four broad levels:
1) Inaccessible - some people cannot get at the content at all.

2) Minimally accessible - everyone can get at the content somehow, but
it may be very difficult. [Approximately WCAG Priority 1 or Section 508]

3) Enhanced accessibility - somewhere between 2 and 4

4) Perfect accessibility - everyone can get at the content easily and
equally easily. Not actually possible for any non-trivial page/site.

Most usability improvements will push a page up through the wide
enhanced accessibility level to some degree, as will most
accessibility improvements.

I would view all usability improvements as accessibility improvements
- because they will be particularly effective for some groups of users.

Most accessibility improvements may also be usability improvements,
because they will give a general (if small) improvement for
everyone. I suspect not quite all.

In practice, perhaps to view them as separate is a bad thing. I can't
think of any circumstance where a (properly implemented) accessibility
increase would lead to a usability decrease, or vice versa.

[1] As defined by software, hardware, disability, aims, or some
combination of the four.

--
Chris