(Source: U.S. Census Bureau, 1996 Survey of Income and Program Participation: August-November 1997) (PDF Format Requires Adobe Acrobat Plug-in)

A person is considered to have a disability if he or she has difficulty performing certain functions (seeing, hearing, walking, climbing stairs, and lifting and carrying), or has difficulty performing activities of daily living, or has difficulty with certain social roles (doing school work for children, working at a job and around the house for adults). A person who is unable to perform one or more activities, or who uses an assistive device to get around, or who needs assistance from another person to perform basic activities is considered to have a severe disability.

7.67 million adults in the United States have impaired vision including color blindness, low-vision, and other vision impairments.

To some 19.47 million adults, walking poses difficulty,  to 6.76 million adults use of a computer  mouse or keyboard is difficult. Even these mobility impairments can be compensated for in good web page design.