SUS: A System Unusable for Twenty Percent of the Population
Summary
Key Insights
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Screen readers allow users to navigate web pages quickly by jumping through well-structured headings and content.
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Low vision users often rely on system-wide screen magnification and color inversion settings to reduce eye strain.
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Alternative navigation methods like head mice and voice dictation are selected based on task and user condition, not used exclusively.
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Traditional lab-based usability research often prioritizes convenience over real assistive technology configurations, leading to inaccurate results.
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Assistive technology users rarely use default settings; they extensively customize tools over time for optimal use.
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The System Usability Scale (SUS) includes questions that confuse assistive technology users and do not capture their true experience.
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Fable’s Accessible Usability Scale adapts SUS questions to better reflect the experience of assistive technology users.
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Initial data shows screen reader users report significantly lower usability scores (mid-50s) compared to screen magnification users (low 60s).
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Users’ lowered expectations after years of experience may mask the true severity of usability issues in assistive technology contexts.
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Measuring accessibility usability accurately enables benchmarking and progress in improving digital products for all users.
Notable Quotes
"I’ve been using screen readers for 30 years and accessibility has always been a passion of mine."
"Screen readers let us jump from one heading to another, replicating the experience of skimming a page visually."
"Low vision users often invert colors and use magnification levels as high as 400 percent to reduce eye strain."
"Alternative navigation users pick different tools based on the task and how they feel at that moment, not just one technology."
"In a usability session, the biggest challenge is not to talk at the same time the screen reader is talking."
"No assistive technology user uses default settings; we spend years customizing everything to work for us."
"The System Usability Scale’s question about needing a technical person to use the system is confusing and inaccurate for screen reader users."
"Most people with my assistive technology might learn to use the system at a different pace than non-disabled users."
"Screen reader users scored significantly lower in usability tests, reflecting the most effort in interpreting content."
"If you’re doing research with people with disabilities, consider using the Accessible Usability Scale to get more accurate insights."
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