The magnitude of disability associated with chronic conditions and aging can be measured from a variety of perspectives. Three of these perspectives—prevalence of chronic conditions and their risk of disability, prevalence of multiple chronic conditions, and limitation in basic life activities—will be discussed here. Because some chronic diseases occur before age 65, and because a life course perspective is important for considering chronic disease, aging, and disability, the data presented are not limited to the elderly.

Prevalence of Chronic Conditions

Although the prevalence of chronic illness increases with age and is a major cause of disabling conditions, many elderly persons are healthy and function independently. In 1988, 33.1 million people in the United States, or 13.7 percent of the noninstitutionalized population, reported some limitation of their activities as a result of chronic disease or impairment; 4.3 percent were limited, but not in their major activity; 5.4 percent were limited in the amount or kind of their major activity, and 4 percent—''the most severely disabled"—were unable to carry on their major activity (Table 6-1) (National Center for Health Statistics, 1989a). The prevalence of all three levels of activity limitation increases with age except for those with "severe disabilities," for whom the rates rise from less than one-half of 1 percent for those under 18 years to 16.2 percent for the 65- to 69-year-olds. For those 70 years and older, however, the prevalence rate falls to 7.6 percent. This reduction may be the result of the oldest old population entering institutions when they become severely disabled.

The prevalence of most chronic health conditions varies by age group. Table 6-2 presents estimates from the 1988 National Health Interview Survey (NHIS) of the number of chronic conditions and the rate per 1,000 persons for all noninstitutionalized persons and for the population aged 65 and older. The conditions are ranked according to their prevalence in the total population. The five most prevalent chronic conditions for all ages are chronic sinusitis, arthritis, high blood pressure, deformity or orthopedic impairment, and hay fever. For the elderly population, arthritis ranked highest with almost half (49 percent) reporting this condition, followed in rank order by high blood pressure (37 percent), hearing impairment (32 percent), heart disease (30 percent), and chronic sinusitis (12 percent) (Figure 6-1). The relative ranking of conditions depends on how the conditions are grouped. For example, if deformities of the back were shown separately, they would rank eighth for all ages and eleventh for the elderly. When combined with deformities or orthopedic impairments of the upper extremities, as shown in Table 6-2, they rank fourth for all ages and seventh for the

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