The Design Gap & The Benefits of Accessible Design

[Note: this page looks at disability and product design through several animations. Use the text links and click “Show Me” to view the animations; the thumbnail images contain alternate text for the animations.]

Looking at disability through the lens of product design, it can be argued that there is no disability until there is an inaccessible product. Disability can be defined as the gap between what a product demands of the user, and what the user is able to provide.

All products make demands upon the user. These demands occur along several dimensions — let’s say there’s vision, hearing, dexterity, cognition, and speech. Products often make demands along more than one of these dimensions at a time.To dial a phone, the user must remember the number, press buttons in the right order, and listen for the ring and answer -- many different performance demands.


Those performance requirements can be very demanding, or easy. Let’s say they can be quantified according to how many people in the total population can perform them with little or no difficulty. The easiest task would be ‘100%’ — everyone can do it. On the other hand, some tasks require so much that only 10% of the population can perform them.Each requirement that the phone demands of the user is shown as a percent, where 50 percent is what the average user can perform.


Now, let’s think about the user. The average user is at 50% for all tasks — an average ability. In this sense, ‘disability’ means anything significantly lower than average, in one or more category of ability.The bell curve shows average ability in the middle, and limited ability a smaller portion at the left.


Let’s say there’s a person who is in the ‘normal’ range for all functions except hearing. How do the demands of the cell phone interact with her abilities?The user's ability exceeds the demands of the phone, except for hearing -- this is the design gap.


So disability, to the extent that it means inaccessibility, results from the interaction between the product and the user. Lowering the requirements can increase the number of successful users.A moving line on the bell curve shows that lower performance requirements results in more successful users.


For each individual there is a set of bell curves with points that indicate their abilities along the different dimensions.A single user shows up as dots on 5 bell curves.

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