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5 December 2011

WAI R&D Symposia » Metrics Home » Report

Symposium Report Summary

The Research Report on Web Accessibility Metrics note format is a [Draft]W3C Working Group Note developed by the WAI Research and Development Working Group (RDWG). It was published in August 2012 at www.w3.org/TR/accessibility-metrics-report/. The latest Editor Draft version, (May 2014), is also available at www.w3.org/WAI/RD/2011/metrics/note/ED-metrics.


Web accessibility metrics are quality ratings that help indicate the level of website accessibility. Metrics are an important tool for researchers, developers, governmental agencies, and end users because they have the potential to communicate accessibility in a simple form, such as a number. A variety of website accessibility metrics have been proposed to complement the A, AA, and AAA levels measurement used by the WAI guidelines. However, the validity and reliability of most of these metrics are unknown so that using them introduces risks, such as relying on confusing or inaccurate ratings. This research report defines and explores the main qualities that website accessibility need to consider, including validity, reliability, sensitivity, adequacy and complexity.

This research report was created following an online symposium held on 5 December 2011 to study how current website accessibility metrics address different quality criteria. The study found out that metrics for which validity quality requirements are established are scarce. Some efforts relating to inter-tool reliability were observed though these do not seem to fully address the quality requirements either. It is important to note that one main outcome of this symposium is that the validity and reliability of web accessibility metrics are, to date, generally unknown. It seems that research in this field is not yet sufficiently mature to provide the necessary methods and tools to compute valid and reliable web accessibility metrics. Another outcome of this research report is a discussion on possible ways forward in accessibility research and development to help reach the necessary maturity point for valid and reliable web accessibility metrics.


M. Vigo, G. Brajnik, J. O Connor, eds. Research Report on Web Accessibility Metrics. W3C WAI Research and Development Working Group (RDWG) Notes. (2012) Available at: www.w3.org/TR/accessibility-metrics-report/

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