Usability is a measure of how easy a system is to use. The goal of website usability is generally to satisfy 95% of site visitors.
Accessibility is a subset of usability. Accessibility means your content can be accessed by all — regardless of technological or physical means. This ranges from visitors with screen readers to those with mobile phones, tablets, or even slow Internet connections.
In the U.S., the CDC estimates ~26% of the population has a disability
Web accessibility means that websites, tools, and technologies are designed and developed so that people with disabilities can use them. More specifically, people can:
1) perceive, 2) understand, 3) navigate, 4) interact with and 5) contribute to the Web.
Web accessibility encompasses all disabilities that affect access to the Web, including:
Web accessibility also benefits people without disabilities, for example:
- people using mobile phones, smart watches, smart TVs, and other devices with small screens, different input modes, etc.
- older people with changing abilities due to ageing
- people with “temporary disabilities” such as a broken arm or lost glasses
- people with “situational limitations” such as in bright sunlight or in an environment where they cannot listen to audio
- people using a slow Internet connection, or who have limited or expensive bandwidth
Federal agencies, federal contractors and agencies receiving federal funds/grants must make their websites accessible. Web Content Accessibility Guidelines (WCAG) is the legal accessibility standard.
The WebAIM Million
97% of home pages had detectable WCAG 2 failures — an average of 51 errors per page
Common types of WCAG 2 failures
|WCAG Failure Type||Level||% of home pages in February 2021|
|Low contrast text||AA||86%|
|Missing alternative text for images||A||61%|
|Missing form input labels||A||54%|
|Ambiguous Links, such as “click here”||A||22%|
Addressing just these few types of issues would significantly improve accessibility across the web.
Website Accessibility Best Practices
- Mobile friendly with valid HTML
- Semantic HTML – e.g. ordered lists, etc.
85.7% of screen reader respondents find heading levels very or somewhat useful
61% of screen readers prefer Word vs. PDF documents (17%)
- Alternate text for all non-decorative images; avoid image-based text (or provide text-based alternatives)
- Site navigation works with a keyboard; and includes a ‘skip to content’ link to bypass navigation
- Avoid: auto-rotating/playing content, such as content sliders; popup windows; links opening new windows; PDF (only) content; ADA overlays and accessibility toggles
- WCAG Quick Reference Level A (minimum requirements)
- Google Mobile Friendly Test
- The WebAIM Million
- WebAIM Screen Reader User Survey
- W3C Easy Checks – A First Review of Web Accessibility
- W3C Accessibility Principles
- ADA accessibility tools:
tot@11y browser bookmarklet, WAVE (Web Accessibility Evaluation Tool), WebAIM Color Contrast Checker, Google (Chrome) Lighthouse
- Accessibility Advocates sign open letter urging people not to use accesibe and other overlay products
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