Trends in Functional Limitations

Everyone knows that we are living longer, but the great unknown—and the subject of some controversy—has been whether older Americans are living in better health. This is not just a matter of personal interest. Policymakers would like to know the answer, as they plan for the retirement of those in the baby boom generation and as they shape the future of the Social Security and Medicare programs.

One aspect of health is the ability to carry out simple physical tasks, and a recent study by RAND researchers Vicki Freedman and Linda Martin finds that the percentage of older Americans with limitations in functioning decreased from 1984 to 1993. This new evidence gives credence to the view that the health of older Americans, as well as their survival, has been improving. In their paper, "Understanding Trends in Functional Limitations Among Older Americans," which was recently published in the American Journal of Public Health, Freedman and Martin explore the factors underlying these trends and attempt to determine whether the trends truly represent changes in the underlying health status of older Americans, or whether they are a result of other influences.

Measuring Functioning

Most studies of trends in the health of older Americans assess whether individuals have difficulty carrying out "activities of daily living," such as bathing and eating, and "instrumental activities of daily living," such as shopping and doing laundry. Using such measures, Manton and his colleagues found declines in disability from the 1980s to the 1990s, but Crimmins and her colleagues obtained mixed results.^[1]

Freedman and Martin note that these measures are potentially influenced by living environments and socially defined roles. For example, the ability to bathe may be facilitated by using a walk-in shower or impeded by having to climb over the edge of a bathtub, and whether an older person is able to do the laundry may depend on that person's expectations about the appropriateness of the task. Thus, aggregate reported changes in the population in the ability to carry out these two specific activities may not represent true changes in underlying health but rather changes in the proportion of older Americans who have the resources to remodel their bathrooms or who think it is appropriate to do their own laundry.

Instead, Freedman and Martin employ four measures—known as measures of functional limitations—that more closely approximate true physiological capabilities and that can be tracked over time for the older American population:

• Difficulty seeing the words and letters in a newspaper
• Difficulty lifting and carrying a 10-pound weight
• Difficulty climbing a flight of stairs
• Difficulty walking three blocks or a quarter of a mile.

These limitations have the additional advantage of being more prevalent in the older non-institutionalized population than difficulties with the activities mentioned earlier. As a result, they provide earlier indicators at the individual level of a possible decline in health.

Functioning Has Improved

Using data from the nationally representative, household-based Survey of Income and Program Participation (SIPP), the researchers analyze changes in the rates of functional limitations for five age groups: 50 to 64 years, 65 to 79 years, 80 and older, 50 and older, and 65 and older. Unlike other studies, they include the 50-to-64 age group because of interest in changes in health at the ages when retirement decisions are often made.

For the period 1984 to 1993, the researchers find large declines in the prevalence of functional limitations across all five age groups. The extent of the improvement varies with age, with the smallest absolute gains occurring among those ages 50 to 64 and the largest occurring among those ages 80 and older. In the aggregate, the population ages 50 and over experienced the following changes:

• 3.7 percentage point decline in difficulty seeing (from 15.3 percent to 11.6 percent)
• 4.6 percentage point decline in difficulty lifting and carrying (from 23.5 percent to 18.9 percent)
• 2.5 percentage point decline in difficulty climbing (from 24.5 percent to 22.0 percent)
• 3.5 percentage point decline in difficulty walking (from 25.8 percent to 22.3 percent).

Of course, the 50 and over population in 1993 may have had different characteristics than the population in 1984. Using logistic regression analysis, the researchers examine the effects of changes in the demographic and socioeconomic composition of the population on the prevalence of functional limitations to see if those changes could explain the improvements. In general, they find that changes in population composition account for only a small portion of the declines in limitations, and the trends—with only three exceptions—remain significantly different from zero, once they recalculate the prevalence rates holding constant the composition of the population. The table shows the recalculated or "adjusted" rates and a list of the factors used to adjust those rates.

For one of the functions—walking—they are also able to control for changes in the use of assistive devices, such as wheelchairs, canes, or crutches. Increases in device use appear to explain improvements in walking for the 80 and older age group, but not the other age groups, after changes in population composition are considered. (Results are not shown.)

Thus, Freedman and Martin are able to home in on a "purer" measure of health and minimize the possible influence of changes in living environments and role expectations over the nine-year period. They factor out the influence of changes in population composition and, for the function of walking, changes in assistive device use. Although they are not able to consider all possible explanations in their models of functioning (e.g., they have no measures of trends in the prevalence of specific diseases and conditions), they factor out many of the possible causes. Accordingly, they conclude that the improvements in functioning strongly suggest improvements in underlying physiological capabilities.

Implications for the Future

The results of this study indicate that the older population today is functioning significantly better than that of just a decade ago. The researchers caution, however, that these downward trends in the prevalence of functional limitations will not necessarily continue. Much work remains to determine the specific physiological causes of the improvements, so it is difficult to predict whether and to what extent the trends will continue. Even if they were to continue, the absolute number of disabled individuals is likely to increase, given the expected growth in the older population. Thus, planning for the needs of a growing number of disabled people will remain a challenge. However, if these downward trends do continue, relatively fewer older Americans will need the medical care and support services associated with limitations, and a greater proportion of the older population should be able to work and live independently.

Notes

• [1] K. G. Manton, L. S. Corder, and E. Stallard, "Chronic Disability Trends in Elderly United States Populations: 1982–1994," Proceedings of the National Academy of Sciences USA, 94:2593–2598, 1997; E. M. Crimmins, Y. Saito, and S. L. Reynolds, "Further Evidence on Recent Trends in the Prevalence and Incidence of Disability Among Older Americans from Two Sources: the LSOA and the NHIS," Journal of Gerontology, 52B:S59–S71, 1997.

Topics

• Geriatrics
• Health-Related Quality of Life
• Older Adults