The population with disabilities is an ambiguous population. Their definition and size depends on the source. Current population sources are the National Health Interview Survey and the U.S. Census Bureau and its three measuring programs. In 1997, these agencies measured the disabled to make up between 13% to 20% of the U.S. population.
Influencing the numbers were poverty, medical advances, the Americans With Disabilities Act, and aging. Emerging conditions such as chronic fatigue syndrome or learning disorders also impact the counting. "A common point of dispute is whether reported increases represent growth in actual incidence, greater awareness, and better surveillance, or simply the reduction of stigma in reporting."
Prevalence estimates for emerging conditions tends to be relatively small. It also varies. Attention deficit hyperactivity disorder, for example, has exploded in the last 10 years and makes up about 3% to 5% of school-age children. Is this growth from increased awareness? Is the growth from improved treatment options? Once again, the absence of a universal definition affects the estimated population size.
"In 1993, sociologist Irving Zola described the futility of pinpointing the exact size of the population with disability, noting that disability represents a set of characteristics everyone shares to varying degrees.' There is dynamism in disability status both because of the transitory character of health and because the connection between a person's impairment and subsequent loss of function is often determined by barriers in his or her physical environment." #1893
Fujiura, G. T. (2001). Emerging trends in disability. Population Reference Bureau.