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The Web Content Accessibility Guidelines (WCAG) 2.0 separate testing into both “Machine” and “Human” audits; and further classify “Human Testability” into “Reliably Human Testable” and “Not Reliably Testable”; it is human testability that is the focus of this paper. We wanted to investigate the likelihood that “at least 80% of knowledgeable human evaluators would agree on the conclusion” of an accessibility audit, and therefore understand the percentage of success criteria that could be described as reliably human testable, and those that could not. In this case, we recruited twenty-five experienced evaluators to audit four pages for WCAG 2.0 conformance. These pages were chosen to differ in layout, complexity, and accessibility support, thereby creating a small but variable sample.

We found that an 80% agreement between experienced evaluators almost never occurred and that the average agreement was at …