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Details of the underlying survey

The calculator uses ‘% excluded’ as shorthand for:

The % of participants from the Towards Better Design Survey (2010), who would not be able to perceive the information comfortably (i.e. quickly and easily), while wearing any visual aids that they would normally wear for the majority of the day.

This survey only had 362 participants, but is particularly appropriate for predicting exclusion associated with artwork that is hand-held because it:

  • Measured near-vision visual ability using a hand-held letter chart, with the prompt: Please identify the smallest row that is comfortable for you to read. Participants were allowed to hold the letter chart at whatever distance they found comfortable, which matches real-world use of handheld artwork.
  • Covered the full range of vision ability within adults aged 16 and over in England and Wales, without pre-screening or focusing on disability and impairment;
  • Measured people's ‘comfort’ vision ability with whatever setup of visual aids they wear for the majority of the day. Using this tool is therefore proposed as being the best way to account for age-related long-sightedness in design assessments.
  • Was postcode sampled, and took place inside people's own homes, in real-world lighting conditions.

This tool intentionally uses survey data that was based on ‘comfort’, to encourage people to design things that are quick and easy to use. However comfort is a very subjective measure, so most survey data on visual ability is instead based on ‘threshold’ data, i.e. what people can see if they try hard. The values of exclusion predicted by this tool are therefore typically higher than other tools that use different data sources.

Many of the people predicted as ‘excluded’ by this tool will in fact be able to see the information, either by finding a reading aid, improving the lighting conditions and/or staring at it for longer. However, these coping strategies compromise the user experience, and we recommend that artwork should be quick and easy to see without requiring coping strategies.

Exclusion calculations are an approximation. However, if an assessor uses this method to compare two designs side-by-side, then the differences in visual clarity that are identified are very real, and the exclusion calculations help to quantify the real-world impact of these differences.



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