How disabilities affect website use

This post follows on from the one on Disability Statistics, and shows how the most common disabilities affect website use.

Reading difficulties

Reading difficulties and dyslexia are extremely common, and affect 15-20% of US adults. Some groups (such as entrepreneurs) have rates approaching 40%.

This group often finds problems with:

  • Large blocks of text
  • Very high contrast text*, such as black text on pure white affects people with Scotopic Sensitivity Syndrome (which makes the letters dance about)
  • Fully justified text aligned to both left and right margins (contains rivers of whitespace which break up the text)
  • Flashing or moving elements, which attract the eye and make it hard to concentrate on reading text

Note that the high contrast required by WCAG 2 checkpoint 1.4.3 can actually cause problems for people with Scotopic Sensitivity Syndrome, and also some low vision users who need to read the screen very close up (put your face next to your screen for 30 minutes on a very high contrast page to see how unpleasant this feels).

Color blindness

Color blindness is also very common, and affects around 8% of caucasian males in the US, but only 0.5% of females. Color blindness comes in many varieties with red-green and blue-yellow color blindness the most common, and inability to see any colors (monochromacy) the rarest.

This group often finds problems with:

  • Text and background colors with little difference in brightness
  • Red text on a green background, or green text on a red background (looks like brown text on a brown background to someone with red-green color blindness)
  • Blue text on a yellow background or yellow text on a blue background

Dexterity difficulties

Problems using hands and arms affects around 7% of the population, and can make using a mouse hard or impossible. Older people are more likely to have dexterity problems due to the onset of arthritis. Even if users can use a mouse, they’ll find it hard to click on small link targets (such as single character links).

This group often finds problems with:

  • Pages that can only be operated with a mouse (e.g. many street mapping websites)
  • Very small links that need very precise motor control to click (e.g. the single character links often used for paging)

Difficulty hearing

This affects around 4-5% of the population, and becomes more common with age. Relatively few websites use audio, so the majority of sites are unaffected. Many office workers are in the same position, since they have no way of hearing website content at work (speakers are very uncommon in offices, and headphones are frowned upon in some corporate settings).

This group often finds problems with:

  • Videos where the audio track is needed to understand the content (e.g. a recording of a TV news bulletin)
  • Standalone audio (e.g. a radio play)

Difficulty seeing

This affects around 3-4% of the population and includes people who are blind and those with low vision who need large print and/or high contrast to read (e.g. people with cataracts or retinal damage caused by diabetes).

Blind people (and some dyslexics) typically use a screen reader, which read out the words on web page, but reading each word out individually is very time consuming so:

  • They use the <title> tag to find out what a page is about before going to the effort of reading it (so the same title on every page is not useful)
  • They often read out all the headings and link text first to figure out what a page is about (screen readers have shortcut keys for this)
  • The use headings inside the page to navigate to the section they’re interested in (so pages without headings are hard to use)
  • They need a quick way to skip navigation links at the top of the page (you don’t want to have to listen to 100 navigation links before hearing the page content)

People with low vision:

  • Often use browser zoom feature to enlarge all the content (normal text enlarges well, but text inside graphics becomes pixelated)
  • May use a custom CSS stylesheet to enlarge text and provide color combinations that work for them (e.g. 24 point yellow text on a black background). This poses difficulties if your pages are unreadable without your site’s CSS stylesheet.

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