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WAI: Strategies, guidelines, resources to make the Web accessible to people with disabilities

Website Accessibility Metrics
Online Symposium 5 December 2011

[ home page & proceedings ]    [ report (W3C Working Group Note) ]

Page Contents


The Website Accessibility Metrics symposium brought together researchers and practitioners to scope the extent and magnitude of existing website accessibility metrics, and to develop a roadmap for future research and development in the field. Details are in the Background and Objectives.


Extended abstracts and slides from the symposium are listed below. See also transcript of the symposium.


Measuring the level of web accessibility is essential for assessing accessibility implementation and improvement over time but finding appropriate measurements is non-trivial. For instance, conformance to the Web Content Accessibility Guidelines (WCAG) is based on 4 ordinal levels of conformance (none, A, AA, and AAA) but these levels are too far apart to allow granular comparison and progress monitoring; if a websites satisfied many success criteria in addition to all Level A success criteria, the website would only conform to level A of WCAG 2.0 but the additional effort would not be visible.

Using numerical metrics potentially allows a more continuous scale for measuring accessibility and, to the extent that the metrics are reliable, could be used for comparisons. However, it is unclear how metrics can be developed that fulfill requirements such as validity, reliability, and suitability. For example, is a web page with two images with faulty text alternatives out of ten more accessible than another page with only one image with a faulty text alternative out of five? While such a count may be a fairly simple and reliable metric it is generally not a valid reflection of accessibility without additional information about the context in which the faults occur, but identifying this context may introduce complexity, reduce reliability, and raise other challenges.

More in-depth background and discussion on web accessibility metrics can be found in the RDWG wiki.


The primary objective of this symposium is to gather, analyze, and discuss practical experience with measuring website accessibility. These may include approaches for measuring 'accessibility in terms of conformance' (metrics that reflect violations of conformance of web content with accessibility guidelines such as WCAG or derivatives such as Section 508) and 'accessibility in use' (metrics that reflect the impact that accessibility issues have on real users, regardless of guidelines). The papers resulting from this symposium will constitute the basis from which to further explore a research and development roadmap for website accessibility metrics.

We particularly welcome discussion of the relationship of these two approaches and how to potentially combine them, as well as a discussion of any of the following types of questions:

Further open research questions and ideas have been identified and we welcome contributions related to any of these too.


The Website Accessibility Metrics symposium was organized by the W3C/WAI Research and Development Working Group (RDWG). Contact Shadi Abou-Zahra (W3C Staff Contact) with questions.

Symposium Chairs

Scientific Committee