(October 2004) Nearly 50 million Americans, one of every five people ages 5 and older, have a disability, according to the 2000 U.S. Census. That number is expected to grow over the next 25 years as the U.S. baby-boom generation enters the ages most prone to disabling injuries and illnesses. Participation in society to the fullest extent possible by people with disabilities, whether young or old, has been a goal of U.S. policies and programs, but translating this aim into reality requires confronting a series of challenges.

One major challenge involves identifying the population with disability. "Disability" refers to an individual's capacity to function within a given social and environmental context. An illness or injury may result in disability for one activity but not another, or for one occupation but not another. A home or work environment can be created or modified to help an individual with disabilities to function more independently. Moreover, disability is not static: A person can develop a short-term disability—for example, due to a fall or stroke—and then recover.

The complexity of the term has given rise to various definitions and indicators, and there is no accepted gold standard for counting the population with disability. The U.S. Census estimates offer a broad overview of the extent of limitation and disability across the nation; nationally representative, well-designed surveys and studies have produced differing but equally credible estimates.

A related challenge involves projecting the number of people who will have a disability and need support in coming decades. Such projections involve debates among experts about the extent to which life expectancy will rise, and whether the risks of developing and recovering from a disability are increasing or decreasing. Over the last few decades, disability appears to have diminished among older people; but it is not clear whether younger people have experienced a similar improvement. At this time, reasons for the decline in disability are not clear, adding to the difficulty in forecasting trends.

The numbers are important because the costs of support systems—both human and technological—for people with disabilities are substantial. At the same time, the benefits of enabling all who live in the United States—irrespective of age or ability—to participate in society are potentially enormous. Disability is associated with reduced workforce participation and related economic consequences. Although the elderly are more likely than the young to develop disabilities, the majority of Americans and the majority of people with disabilities are of working age. About equal numbers of people with disabilities are men and women. Minorities, the very old, the poor, people who are divorced or separated, and people living in the South have an especially high rate of disability.

There is a growing array of support systems to help people with disabilities participate in school, work, and leisure activities, and for older people to maintain independent living. Technological innovations are expanding and may support some of the tasks that now require human assistance. A variety of federal assistance programs exist for children, adults, and the elderly. Newer policies and programs emphasize legal protections for individuals with disabilities and the removal of barriers to participation. These policies require, among other things, changes to entryways and the inside of public buildings, and they promote the use of technological aids by people with disabilities. The goal of such programs is to allow all members of society, irrespective of age or ability, to participate in a meaningful way in American society.

Understanding disability is an important step in ensuring that Americans of all ages and abilities have the opportunity to participate fully in society.

Vicki A. Freedman is director of Polisher Research Institute of the Madlyn and Leonard Abramson Center for Jewish Life, in Philadelphia. Linda G. Martin is a scholar in residence at the Institute of Medicine. Robert F. Schoeni is senior associate research scientist at the Institute for Social Research, and associate professor of economics and public policy, University of Michigan.