prevalent; over the same period, however, mortality rates declined for 8 of those diseases. Increased morbidity and declining mortality trends in chronic conditions for the elderly were similar. Verbrugge also noted an increase since the late 1960s in limitation of activity. She suggests that these increases may be caused by a variety of factors: there may be changes in "true" incidence and survival rates, individuals may be more accepting of and accommodating to their conditions, and they may be more likely to adopt the sick role than in the past.
Using data for nine commonly reported chronic conditions from the 1984 Supplement on Aging of the NHIS, Guralnik and colleagues (1989b) showed that the prevalence of comorbidity (multiple conditions) is substantial among the population aged 60 and older. High rates of comorbidity were reported for women, with prevalence rates rising from 45 percent in the age group 60 to 69 years to 70 percent in those 80 years and older. For those 60 years of age and older who had no chronic conditions, only 2.1 percent of men and 2.3 percent of women required assistance in performing one or more activities of daily living (ADLs). These rates increased to 8.6 percent for men and 6.9 percent for women who had 2 chronic conditions and to 22 percent for men and 15.7 percent for women who had 4 chronic conditions. In addition, there was a clear association between the number of conditions and the proportion of people with disability as assessed by inability to perform activities or self-care. The authors found that, for the most commonly reported pairs of comorbid conditions (i.e., high blood pressure and arthritis), the observed coprevalence was consistently higher than expected. Possible explanations for this finding include (1) detection bias (those with one condition may have more contacts with the medical care system and a greater likelihood of being diagnosed with a second condition); (2) response patterns (people who report one disease may be more likely to report having other diseases); and (3) biological basis (genetic and environmental factors may increase susceptibility to disease).
Measures of functioning in basic life activities, including ADLs and instrumental activities of daily living (IADLs), are important indicators of health status and disability. Analysis of data from the 1979 and 1980 Home Care Supplement to the NHIS shows 5.4 million persons who reported needing assistance in ADLs or IADLs; of this total, 43 percent were under age 65 (LaPlante, 1989b). Middle-aged adults who need assistance are somewhat more likely than either children or older adults to use equipment and to be less dependent on help from others. Children and people aged 85 and older are also more likely to need assistance in multiple activities and to need help from others more often.