social interaction. Also, the effects of specific stages in the model can be moderated by such interventions as assistive devices. Similarly, environmental modification (e.g., elimination of physical obstacles and barriers) is an important form of disability prevention, as is such landmark antidiscrimination legislation as the recently enacted Americans with Disabilities Act.

A variety of personal, societal, and environmental factors can influence the progression of a disabling condition from pathology to disability. They can also affect the degree of limitation or disability a person experiences and the occurrence of secondary conditions. A few of these factors are health status, psychological state, socioeconomic status, educational attainment and vocational training, climate, and the presence of multiple conditions and disabilities.

As indicated in the model, quality of life is an integral part of the disabling process. Research indicates that a person's perception of quality of life influences his or her responses to potentially disabling conditions and therefore outcomes. In turn, each successive stage in the disabling process poses an increasing threat of diminished quality of life. Measures that reduce this threat—for example, providing assistive technology that enables an individual to remain autonomous in at least some roles or modifying the work site to accommodate a person's limitations—can be effective interventions for preventing disability.

Thus disability is the product of a complex interactive process involving biological, behavioral, and environmental (social and physical) risk factors, and quality of life. Although disability always begins with a pathological condition, it is not inevitable even for people with incurable diseases or injury-caused conditions that carry the highest risks. There are usually, if not always, many points in the progression to disability at which to intervene and improve the quality of life for people with potentially disabling conditions.

The next four sections briefly discuss some of the information from each of the focus chapters. In the full report, these chapters each cover the magnitude of disability related to that category of disability, data needs, and prevention strategies. Although some primary prevention measures are described and discussed, the emphasis in the chapters and in these sections is on prevention for people who already have potentially disabling conditions (i.e., secondary and tertiary prevention).

Developmental disabilities affect about 4 percent of the population under age 21 and are caused by a variety of conditions, including cerebral palsy, seizure disorders, mental retardation, hearing and vision impairments, autism, structural birth defects (e.g., spina bifida) that cannot be corrected by