that functional limitation and disability resulting from chronic diseases and mental disorders can be measured and changes in the prevalence of these conditions can be monitored over time.

Multiple Chronic Conditions

Multiple chronic conditions have a significant impact on disability status. Many people, especially the elderly, have multiple chronic and potentially disabling conditions. Data from the NHIS for the three-year period from 1979 to 1981 indicate that multiple chronic conditions causing limitation of activity increase with age. For example, among those who report chronic conditions that cause limited activity, only 15 percent of the group under age 17 reported more than one condition; this proportion increased to 40 percent for those aged 75 and older (Rice, 1989).

In recent years, more people are reporting that they have chronic conditions that limit their activities. Analysis and comparison of the NHIS data from two three-year periods, 1969-1971 and 1979-1981, showed that the prevalence rate of limitations in activity increased significantly (Rice and LaPlante, 1988a). The rate increased more than one-fifth, from 119 to 145 per 1,000 persons, for the entire noninstitutionalized population, with greater increases for women than for men. The largest increases occurred for children and youth and for middle-aged persons, 45 to 64 years of age, especially for the "most disabled"—those unable to carry on their major activity. The prevalence rate of limitation declined slightly in later years (ages 75 and over), indicating that the health of the very old living in the community may have improved slightly. Comparison of health indicators over time for the very old, however, must account for changes in institutionalization, and this factor was not addressed in that report.

People with disabling conditions reported more chronic conditions and more days of restricted activity over the ten-year period 1969-1971 to 1979-1981. The number of chronic conditions per person causing limitation of activity increased 12.5 percent, from 1.32 to 1.48 per person with increases reported for all ages (Rice and LaPlante, 1988a). The greatest increase was for noninstitutionalized persons aged 85 and older, suggesting worsening health as the probable explanation. In general, the more severely limited population reported the greatest increases in multiple chronic conditions, which suggests that persons may be living longer with severely limiting chronic conditions.

Other researchers have found similar trends. Verbrugge (1984) analyzed past trends in specific chronic conditions, in disability (as defined by activity limitation), and in mortality for middle-aged and older persons reported in the NHIS over a 23-year period, 1958 to 1981. For middle-aged people, 10 of the 11 chronic diseases with high mortality rates had become more

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