opment of secondary health conditions and limit the effects of atypical or premature aging among young adults with disabilities (see Chapter 5).

To provide insight into the future of disability, this chapter reviews recent trends in the amount, type, and health-related causes of disability—primarily in the form of activity limitations—for people in early, middle, and late life. It considers projections of future levels of disability. The analysis here should be read in the context of the review in Chapter 2 of the inadequacies in the nation’s current disability surveillance system. As in 1991, when the Institute of Medicine (IOM) report Disability in America was published, data sources that can be used to guide the future of disability in America, particularly efforts to identify and remove environmental barriers to participation for people with disabilities, are inadequate.

Current statistics, discussed further below, indicate that the number of people with disability (broadly defined as impairments, activity limitations, or participation restrictions) now exceeds 40 million—and that number could be more than 50 million. Data on trends in disability during early, middle, and late life present a mixed picture of the changes that have taken place during the last two decades and more. Among children, evidence points to increases in some health conditions—including asthma, prematurity, autism, and obesity—that contribute to disability. These increases have been accompanied by increases in certain activity limitations that are not entirely explained by increased health and educational screening of children. The percentage of adults under the age of 65 who had activity limitations, including work limitations, grew during the 1990s, although this increase appears to have leveled off recently. In contrast, among older adults, declines in the prevalence of personal care and domestic activity limitations have been reported, although not all groups appear to have benefited equally, and the reasons for these declines remain unclear.

As described in Chapter 2, data on participation restrictions, in particular, remain relatively limited. Thus a full portrait of trends in disability is not possible. Moreover, although the equalization of opportunities for people with disabilities is an increasing focus of researchers, they cannot yet track the broad range of environmental factors that contribute to activity limitations and participation restrictions. This chapter focuses on trends during the past two decades in a relatively narrow set of activity limitations, the health conditions that contribute to those limitations, and, where relevant, possible explanations for these trends.

CURRENT ESTIMATES OF DISABILITY AND RELATED CONDITIONS

As discussed in Chapter 2, the omission of key groups from national population surveys has important implications for the development of basic



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