The Effects of "Not Knowing What You Don't Know" on Web Accessibility for Blind Web Users
Jeffrey P. Bigham, Irene Lin, Saiph Savage · 2017 · Proceedings of the 19th International ACM SIGACCESS Conference on Computers and Accessibility (ASSETS '17) · doi:10.1145/3132525.3132533
Summary
This paper introduces and empirically investigates the concept of "Not Knowing What You Don't Know" (NKWYDK) in the context of blind web users. When a blind person encounters difficulty finding information on a web page, they face a fundamental uncertainty that sighted users rarely experience: is the information present but inaccessible (hidden behind an image without alt text, requiring a mouse click, etc.), is it present but hard to find (poor information architecture, missing headings), or does it simply not exist on the page? Sighted users can typically resolve this quickly through visual scanning, but blind users relying on screen readers must navigate content linearly or through structural elements, making it much harder to determine the source of their difficulty. The researchers designed a controlled study with 60 participants — 30 sighted and 30 blind — who each completed 8 information-finding tasks across 8 different web pages. Tasks were designed at four difficulty levels: Easy (information readily findable), Hard (information present but hidden or poorly structured), Inaccessible (information technically inaccessible to screen readers), and Impossible (information does not exist on the page). The study was conducted remotely so blind participants could use their own screen readers and settings, increasing ecological validity.
Key findings
Blind participants spent similar amounts of time on Inaccessible tasks (172.5 seconds average) and Impossible tasks (223.7 seconds), demonstrating the core NKWYDK problem — they could not distinguish between information that was present but inaccessible and information that did not exist. Sighted participants, by contrast, completed Inaccessible tasks in 84.2 seconds but took 110.6 seconds on Impossible tasks, showing they could differentiate more effectively. Nearly all blind participants (95.1%) completed Easy tasks successfully, but success dropped sharply to 37.7% for Hard and 24.6% for Inaccessible tasks. Critically, blind participants frequently misidentified the source of their problems: they confused Hard, Inaccessible, and Impossible categories, while sighted participants accurately categorised task difficulty. Blind users blamed bad HTML design 31% of the time and blamed themselves 13% of the time, with 25% attributing problems to web accessibility issues. Some "power users" among blind participants employed sophisticated workarounds — examining HTML source, checking CSS font colours, using OCR plugins — to solve technically inaccessible tasks, but these strategies required advanced technical knowledge inaccessible to most users. Overall, blind users required approximately twice as long as sighted users across all task types.
Relevance
This paper reframes web accessibility beyond the binary of "accessible or not" by identifying a deeper problem: the uncertainty blind users face about why they cannot find information. This has direct implications for web developers and accessibility practitioners. First, it argues that WCAG compliance alone is insufficient — severe usability problems create effectively the same barriers as technical inaccessibility. Second, it suggests that tools exposing accessibility metadata to users (e.g., indicating how much content on a page is in images, whether elements require mouse interaction) could help blind users make better decisions about where to invest their time. Third, the finding that blind users blame themselves 13% of the time for problems caused by inaccessible design highlights the psychological cost of poor accessibility. The study's limitations include a technically savvy blind participant pool and use of controlled rather than in-the-wild web pages, but the NKWYDK framework offers a valuable lens for understanding accessibility barriers across disability types.
Tags: web accessibility · screen readers · blindness · usability · information foraging · user research
Standards referenced: WCAG 2.0