Web accessibility has so many benefits that I really do wonder why such a large number of websites have such diabolically bad accessibility. One of the main benefits is increased usability, which according to usability guru, Jakob Nielson, can increase the sales/conversion rate of a website by 100% and traffic by 150%.

At which point you must surely be asking, “So if I make my website accessible its usability will increase and I'll make more money out of it?”. Well, not quite. An accessible website is not automatically more usable but there are many areas of overlap:

1. Descriptive link text

Visually impaired web users can scan web pages by tabbing from link to link and listening to the content of the link text. As such, the link text in an accessible website must always be descriptive of its destination.

Equally, regularly sighted web users don't read web pages word-for-word, but scan them looking for the information they're after.

Link text such as 'Click here' has poor accessibility and usability as both regularly sighted and visually impaired web users scanning

the paragraph will take no meaning from this link text by itself. Link text that effectively describes its destination is far easier to scan and you can understand the destination of the link without having to read its surrounding words.

2. Prompt text assigned to form input

In order to make forms accessible we need to assign the prompt text to its form item. THis is especially useful when done with checkboxes and radioboxes, as the text becomes clickable too. Checkboxes and radioboxes are small and pernickety for even the steadiest of hands so by increasing the clickable region everyone benefits.

3. Large chunks of information divided up

There are a number of techniques that can be taken to increase the usability for visually impaired users, who have to listen to the information on each page and try to remember it. By structuring information into small, manageable groups, enhanced usability for these users can be achieved.

Methods to accomplish this can include using sub-headings to break up body content, grouping form items with the fieldset command and using lists. Breaking down groups of information is obviously highly useful for sighted web users too, as it greatly enhances our ability to scan the screen quickly.

4. Site map provided

Site maps can be a useful accessibility tool for visually impaired users as they provide a straightforward list of links to the main pages on the site, without any of the fluff in between. Site maps are of course useful for everyone as they provide us with a way of finding pages quickly and help us visualise the structure of the website.

5. Simple and easy language

From an accessibility point of view, this one's important for people with reading and/or cognitive disabilities and site visitors who's first language isn't the one you're writing in. From a usability point of view, well, it helps everyone. Reading from computer screens is tiring for the eyes and about 25% slower than reading from paper. As such, the easier the style of writing the easier it is for site visitors to absorb your words of wisdom. Wherever possible shorten your sentences. Use, ‘apply' instead of ‘make an application' or ‘use' instead of ‘make use of'.

6. Consistent navigation

Having consistent navigation across pages is also important for maximising accessibility to people with reading and/or cognitive disabilities, but again everyone benefits. Each time you visit a new website it takes you a few seconds to adjust to the unique layout and user interface of that page. Well imagine if you had to do that every time you follow a link to a new page!

By having a consistent interface across a website we can instantly locate the navigation and page content without having to look around for it. In reality, most sites do have consistent navigation across most pages. The main culprit for falling foul of this guideline is the homepage, which some websites structure quite differently to the rest of the site. By having a consistent interface across the entire website we can instantly locate the page content without having to look around for it.

7. No unannounced pop-ups

For web users utilising screen readers pop-ups can be a real accessibility nuisance. Screen readers read out the content of whichever window is on top of the others. Pop-ups display over the top of the main website so will always be read out first. For visually impaired users this can be frustrating as they may not realise that what they're hearing isn't the ‘real' website.

So, pop-ups are bad for accessibility. As for usability, well I'm sure you hate pop-ups as much as I do. Many toolbars, such as the Google toolbar, now come packaged with a pop-up blocker so allow you to surf the web without the irritation of new windows popping up.

8. CSS used for layout

CSS-based sites are generally have a greater ratio of content to HTML code so are more accessible to screen readers and search engines. Websites using CSS for layout can also be made accessible to in-car browsers, WebTV and PDAs. Don't underestimate the importance of this - in 2008 alone there'll be an estimated 58 million PDAs sold worldwide (source: http://www.etforecasts.com/pr/pr0603.htm).

As well as improved accessibility, CSS-based websites have one large usability benefit: increased download speed. Broadband isn't as widespread as you may think. In the UK for example, just one in four web users are hooked up to broadband (source: http://www.statistics.gov.uk/pdfdir/intc0504.pdf) so improving the download speed of your web pages could provide a great usability advantage over your competitors.

9. Transcripts available for audio

One group of web users with special accessibility needs that doesn't get much press is hearing impaired users, who need written equivalents for audio content. Providing transcripts is in fact highly beneficial to all users. Many of your site visitors probably can't be bothered to wait for your 3Mb audio file to download and start playing. They may prefer just a quick outline of what's contained in the audio content.

By providing a transcript, broken up by sub-headings and with the key terms highlighted, non-disabled site visitors can skim through it and get a general idea of the content. They can then make a more informed decision about if they want to wait for the 3Mb audio file to download.

10. Screen flickering and movement avoided

Some epileptic web users must be careful to avoid screen flicker of between 2 and 55 Hz. Web users with reading and/or cognitive disabilities and those using screen magnifiers will struggle to keep up with scrolling text (if you do have scrolling text be sure to provide a mechanism to stop it).

In addition to being a bad idea for accessibility, neither flickering nor scrolling text are good for usability either. The former can be distracting when you're trying to read something and you see flashing out the corner of your eye; the latter isn't good either as you have to wait for the content to slowly appear. When you see scrolling text do you usually bother to stop what you're doing so you can read it as it gradually materialises? Or do you ignore it?

The other disadvantage of scrolling or changing text is that you might see something you want to click on, but before you know it it's gone. And now you have to wait 30 seconds for it to re-appear again!

Conclusion

With all this overlap between web usability and web accessibility there's no excuses for not implementing basic accessibility on to your website. Outside of the ethical argument there are many reasons to make your website accessible, one of the main one being that its usability will be improved. No one can argue with that.