are dismissed as highly doubtful. The elderly are viewed as being in a state of inevitable physical and mental decline, resulting in a deteriorating quality of life and, eventually, total dependence. Indeed, about 80 percent of people age 60 and older have at least one chronic disease (Guralnik et al., 1989b), and about 40 percent of those age 65 and older have an activity limitation, including the 17 percent who require assistance in performing some basic life activities (LaPlante, 1989b). Yet to view people in late adulthood as being in an irreparable state of decline is to ignore the tremendous diversity among individuals who are collectively identified as the elderly.
As the committee's model of the disabling process suggests, there are numerous opportunities for intervening and modifying the risk factors that predispose people with chronic diseases to disability. Obviously, the goals of preventing, or at least delaying, the onset of disability and of minimizing the severity of its consequences become more challenging as the age of the target population increases and as the risks of chronic disease, comorbidity, and functional limitation also increase. As mentioned earlier, from age 55 onward, the risk of requiring assistance in basic life activities rises sharply, and by age 85 the risk of disability approaches 50 percent. Still, disability is not a fait accompli even among the oldest of the elderly.
At issue is not whether preventive interventions are beneficial but rather what those interventions should be and how they should be evaluated. Traditionally, the evaluative standard has been improvement in health status. But this standard, borrowed from acute care, is too confining to guide development and assess the effectiveness of prevention measures for chronic disease and disability. A more appropriate standard is quality of life, of which health status is one component. Even when functional capacity cannot be restored, it is indeed possible to improve well-being and to facilitate personal autonomy by addressing factors in an individual's social situation.
The fields of gerontology and geriatrics recognize the importance of interventions to achieve the broader goal of improving quality of life. In these fields, the concept of successful aging has been advanced to expand the focus of practitioners beyond health status to include assessments of the quality of day-to-day life. Successful aging, or aging well, does not imply freedom from disabling conditions. One is aging well when one maintains a satisfying sense of continuity and can fulfill expectations of personal independence and social participation. Despite the physiological and psychological stresses that can accompany advancing age, many older adults have the vitality and resilience to function at a high level. Moreover, frailty and dependence need not preclude a reasonable quality of life. Conversely, a low quality of life can affect the likelihood of developing a disability. Just as among younger age groups, the risk of disability among the elderly is associated with poverty, inadequate education, poor housing, and social isolation.
Therefore, effective management of chronic disease requires an approach