Chris Jasek of Elsevier's User-Centered Design Group answers your usability questions
How can I improve the accessibility of my website?
Accessibility in this context refers to the universal ability of the user population to navigate and access features and content of a website. Users may have a visual impairment or a motor difficulty that requires them to access the Web via special software such as screen magnifiers, screen readers and Braille displays. Sometimes users may need to access a site using a text-only browser or without using a mouse.
Here’s a list of some of the most common changes you can make to a website to improve its accessibility.
- Don’t specify fonts in absolute point or pixel sizes (e.g., 10pt, or 13px). Instead use relative size measures (e.g., x-small, small, medium, large, x-large).
- Don’t use the site logo or home button as an active link on the home page itself.
This helps users confirm that they are actually on the home page.
- Do use an ALT tag for every image on your web pages. An ALT tag is something you can specify in HTML as part of an image. It’s meant to specify an ALTernate text that can be displayed when the image itself might not be viewable (i.e., browser has images turned off or user using a screen reader). ALT text can be seen by a user when they mouseover an image. The ALT text used should accurately describe the image. If the image is purely cosmetic use “ALT=""” (an empty string).
- Do provide skip navigation for repetitive navigation bars. Usually this applies to the main navigation bar, placed on the top of all Web pages. Skip navigation provides an invisible link before the navigation bar that jumps down the page to where the real content begins. This link is invisible to the eye, but not to screen reader software, and so screen reader users can choose to skip over the reading of repetitive navigation links and get right to the content they need.
For more information and additional tips to improve accessibility visit:
www.diveintoaccessibility.org
www.webaim.org/standards/508/checklist 
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