E: Definition of User Population Served by the Accessible Design Community
Introduction
Numerous sources address the issue of types of impairments faced by consumers with disabilities. The types of impairments include visual, auditory, motor, and cognitive. This includes all age ranges and cultures. The difficulty in the characterization of any particular impairment is that there is so much variability in the degree and extent of impairments in the community of individuals with disabilities. For example, the capabilities of someone with low vision are clearly different than the capabilities associated with someone without vision. In addition, the variability of the capabilities associated with a particular type of impairment can depend on the circumstance of the impairment. For example, the capabilities associated with someone that has been blind from birth are quite different from the capabilities associated with someone who has recently lost vision.
Designers would benefit greatly from a thorough documentation of the capabilities and limitations of users throughout the range of common impairments. After all, user-centered design is based on a thorough understanding of the user. Without this knowledge the designer is forced to either not take the community of people with disabilities into account or to utilize a partial understanding of the user base in the development of new products.
It is clear that the community of people with disabilities consists of a sizable portion of the US population. The following table, with information gathered from Kaye (1997, 1998) and McNeil (1997) provides an overview of the community of people with disabilities in the United States:
Table 3: Characterization of the Disabled Community in the United States.
| Number of Americans with a disability | 54 million |
| Number of those in institutions | 2 million |
| Number age 15+ with visual limitations | 8.3 million |
| Number age 15+ with hearing limitations | 9.7 million |
| Number age 15+ with speech limitations | 2.0 million |
| Number age 15+ with lifting/carrying limitations | 16 million |
| Number age 15+ with self care limitations | 8.2 million |
| Number age 15+ with home management limitations | 12.3 million |
| Number working age adults restricted in working ability | 19 million |
| Unemployment rate of working adults with any activity limitation | 48% |
| Unemployment rate of working adults with severe functional limitation | 74% |
| Unemployment rate of working adults with work disabilities | 72% |
| Percentage of disabled living in poverty | 30% |
| Percentage of disabled without a high school education | 38.4% |
| Percentage of disabled living in metropolitan area | 74.8% |
| Percentage of disabled who feel social isolation is problematic | 51% |
| Percentage of disabled who have public facility access problems | 24% |
| Percentage of disabled who are of working age | 57.6% |
| Percentage of disabled over age 65 | 31.6% |
| Percentage who acquired their disability before age 20 | 21% |
| Percentage who acquired their disability after age 40 | 53% |
E-1. What types of impairments do consumers with disabilities face?
Since accessibly designed products are expected to be accessible to people with the widest range of abilities in the widest range of circumstances, consumers of such products may have profound cognitive, perceptual, emotional and/or movement impairments or no impairments at all (ABLEDATA, 1994, 1995, 1999; Vanderheiden, 1997). Impairment might be temporary (e.g., a broken arm or difficulty speaking the dominant language) or long-term (e.g., paralysis or deafness). King (1999) notes that the nature of an individual’s impairment can change daily or even hourly. Vanderheiden (1997) notes that an individual can have multiple impairments. Additionally, some impairments grow worse over time (e.g., cognitive impairment due to dementia or perceptual impairment due to aging, Fisk & Rogers, 1997). Finally, millions of individuals partially compensate for impairment through the use of assistive devices (Russell, et al, 1997), and ability should be examined both with and without the use of such devices (Vanderheiden, 1997). The accessibility of a product may depend on how well it accommodates a particular assistive device (e.g., Brodin, et al, 1999; Engelen, et al, 1999; Wilson, 1996).
For the purposes of accessible design, however, Vanderheiden (1997) organizes impairment into five broad categories, based on the impact of the impairment on the use of commercial products. The categories are: visual impairments, hearing impairments, physical impairments, cognitive or language impairments, and seizure disorders. The severity of impairment within each category varies, and an individual may have impairment spanning multiple categories. People with visual impairments experience difficulty when using visual displays, reading visual output, particularly written or printed instructions or other documentation, and using controls whose labels are coded with text or color. People with hearing impairments have difficulty perceiving auditory information present in displays or used as control feedback. Physical impairments may be either neuromuscular (e.g., paralysis or spasticity) or skeletal (e.g., arthritis or missing limbs), and the functional limitations caused by either type vary widely. Like physical impairments, cognitive impairments also vary widely in their implications for functional limitations. Seizure disorders affect the continuity of movement, and can be triggered by particular display types (i.e., those including rapidly flashing (10-25 Hz) lights).
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