Usability and Accessibility


Usability is the measure of the quality of a user's experience when interacting with a product or system. Usability is a combination of factors that affect this experience, including:

  • Ease of Learning - How fast can a user who has never seen the user interface before learn it sufficiently well to accomplish basic tasks?
  • Efficiency of Use - Once an experienced user has learned to use the system, how fast can he or she accomplish tasks?
  • Memorability - If a user has used the system before, can he or she remember enough to use it effectively the next time or does the user have to start over again learning everything?
  • Error Frequency and Severity - How often do users make errors while using the system, how serious are these errors, and how do users recover from these errors?
  • Subjective satisfaction - How much does the user like using the system?

Usability Testing

The goal of usability testing is to ascertain what will help users accomplish their tasks and what may impede them. Using the prototype as a starting point, the usability testers build a set of scenario tasks they will ask users to attempt. As detailed information about user success is gathered and reported, the prototype can be modified and additional aspects of that prototype tested.

Usability testing can be done inexpensively or more formally, depending on the size and budget of the site under development. When the site has been implemented, it is incumbent on the developers or the owners of the content to assess its performance by analyzing reports, usage logs, and other data sources for the site and by continuing to gather user feedback on usability.

(Copyright 2006. U.S. Department of Health and Human Services. )

Related Resources


The practice of web accessibility allows all users, including those with disabilities, to access complete website content. Web accessibility encompasses all disabilities, including visual, auditory, physical, speech, cognitive, and neurological disabilities.

A key principle of accessibility is designing websites and software that are flexible to meet different user needs, preferences, and situations. This flexibility also benefits people without disabilities in certain situations, such as people using a slow Internet connection, people with "temporary disabilities" such as a broken arm, and people with changing abilities due to aging.

The World Wide Web Consortium (W3C) develops strategies, guidelines, and resources to help make the web accessible. For more information, visit the Web Accessibility Initiative (WAI) at

Quick Tips

The following ten "Quick Tips" summarize key concepts of accessible web design, and are not complete guidelines. For more information, including explanations, strategies, and detailed markup examples, visit

  1. Images and animation. Use the alt attribute to describe the function of each visual.
  2. Image maps. Use the client-side map and text for hotspots.
  3. Multimedia. Provide captioning and transcripts of audio, and descriptions of video.
  4. Hypertext links. Use text that makes sense when read out of context. For example, avoid "click here."
  5. Page organization. Use headings, lists, and consistent structure. Use CSS for layout and style where possible.
  6. Graphs and charts. Summarize or use the longdesc attribute.
  7. Scripts, applets, and plug-ins. Provide alternative content in case active features are inaccessible or unsupported.
  8. Frames. Use the noframes element and meaningful titles.
  9. Tables. Make line-by-line reading sensible. Summarize.
  10. Validate. Check your work. Use tools, checklists, and guidelines.

Reprinted with Permission. Introduction to Web Accessibility v. 2.0 September 2005, S.L. Henry, ed. Copyright 2005 World Wide Web Consortium, (Massachusetts Institute of Technology, European Research Consortium for Informatics and Mathematics, Keio University). All Rights Reserved.

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