We undertook a study of validity and reliability of WCAG 2.0 and found that an 80% target for agreement is not attainable, when audits are conducted without communication between evaluators. Even with experienced evaluators the error rate is relatively high; and further, untrained accessibility auditors -be they developers or quality testers from other domains- do much worse than this. Read the full published text via ACM Author-izer Open Access on the publications page.