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Measuring the level of accessibility of websites is essential for assessing 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 website 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 to 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.

This Special Thematic Session (STS) is a continuation of the W3C/WAI Online Symposium on Website Accessibility Metrics held on 5 December 2011. It invites further, more detailed contribution and discussion on experiences 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) and 'accessibility in use'. More in-depth background and discussion on website accessibility metrics can be found in the RDWG wiki.

This STS particularly welcomes 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:

• What sort of techniques can we explore to combine metrics that are computed automatically, semi-automatically (with input from humans), and manually (where the judgment is made by humans, even if with input from software)?
• How can we build an infrastructure (such as IBM Social Accessibility) that allows experts to store accessibility information (metadata) for use with metrics that are computed during subsequent audits?
• What metrics, or combination of metrics, can be used as predictors of accessibility?
• How shall we characterize the quality of such predictors in terms of properties such as reliability, validity, sensitivity, adequacy and adaptability?
• Which approaches can be embraced for validating, benchmarking, and comparing web accessibility metrics?
• How should we tackle metrics in web applications with dynamic content?

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

Acknowledgements: This Special Thematic Session (STS) is jointly organized by the EC-funded WAI-ACT Project and is a continuation of the W3C/WAI Online Symposium on Website Accessibility Metrics held on 5 December 2011.

Chair:

Shadi Abou-Zahra, W3C/WAI

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Submission:
Contributions to a STS have to be submitted using the standard submission procedures of ICCHP at:
https://secure.icchp.org/tool/login.htm When submitting your contribution please make sure to select this STS under "STS/Session".
Contributions to a STS are evaluated by the Programme Commitee of ICCHP and by the chair(s) of the STS.
Please get in contact with the STS chairs for discussing your involvement and pre-evaluation of your contribution.
Submission Deadline: February 1, 2012