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COMMENTARY |
1 Polisher Research Institute, Horsham, Pennsylvania.
2 Population Council, New York, New York.
Address correspondence to Vicki A. Freedman, PhD, Polisher Research Institute, 1425 Horsham Rd., North Wales, PA 19454. E-mail: vfreedman{at}abramsoncenter.org
We read Robine and Michel's (1) article with great interest, and applaud their efforts to integrate the growing body of literature on trends over time in mortality, health, and disability of older populations. As the number and proportions of older people grow around the world, the desirability of a unifying theoretical framework to understand the interplay of these processes and their trajectories over time at the population level has never been greater. These trends will have important consequences for the provision and financing of health care and the abilities of older people to continue to play productive roles at work and in society.
That said, moving beyond theories of population change related to the basic health processes of morbidity and mortality to theories that encompass disability is extremely difficult. Although Myers and colleagues (2) and now Robine and Michel (1) provide important insights, here we highlight one complication that will likely prove challenging in incorporating disability into models of health change at older ages: the environmental and social elements inherent in the measurement of disability.
Unlike health and mortality, which are ultimately intrinsic characteristics of individuals in a population, disability is fundamentally a social construct. Although several classification schemes and frameworks have been developed to explicate the disablement process at the individual level (3–6), there is no agreed-upon definition or measure of this concept.
Broadly conceived, the term refers to the individual's capacity to function or carry out a role in a given social and environmental context. Disability exists when the demands of a particular context do not match an individual's physical, cognitive, and psychological capacity. So, for example, an older woman who cannot lift her leg off the ground high enough to climb into a bathtub may have a personal care disability if she lives in a home with a bathtub, but not if she lives in a home with a walk-in shower. At the individual level, morbidity does not necessarily result in disability; on the contrary, through changes in the environment, accommodations, and simple changes in behavior, disability may be largely avoidable, at least until very close to death.
Measuring disability in surveys is particularly challenging. Given questionnaire constraints, survey researchers typically probe only select aspects of the disability nexus, and, depending on the choices made, results may not be comparable from one survey to another. In some instances, the questions refer to the unaccommodated (or "underlying") capacity—that is, how a task could be performed in a specific environment without technological or human assistance. In other cases, the ability to function with supports—technological, human, or both—or the actual use of those accommodations is of interest. So, to continue with the example, the older woman who reports using a stool and grab-bar in her walk-in shower might report difficulty if she were asked about bathing without help or the use of aids. But if she were simply asked are you able to or do you need help to bathe, she might respond no and be classified as not having a disability.
Ignoring these and other distinctions in survey design may lead to apparent inconsistencies in disability trends. Such has been the case for United States trends in activities of daily living from the mid-1980s to 2000 (7). Last year, we participated with a dozen fellow demographers and disability researchers in a workshop sponsored by the National Institute on Aging, which found that trends were indeed sensitive to definition including notions of assistance and technology aids, and that once these definitional nuances were taken into account, a more coherent picture of disability decline was evident for the 1990s. This effort focused on only one country, one 15-year period, and one type of disability, but underscored that not all disability measures and concepts are equivalent (8). Robine and Michel's review of the international evidence on disability trends does not provide enough detail to explore this point further (1), but it would be worthwhile to reexamine such studies with an eye for these distinctions.
Beyond clarifying definitions and measures of disability, new theories governing the movement of population-level morbidity, disability, and mortality processes must incorporate theoretical perspective on changes in the nonhealth elements of disability. At the population level, how a disability curve shifts as a population ages involves understanding not only initiatives that may alter the morbidity trajectories of individuals but those that affect the living environments, technological adaptations, and social programs available to older people. We join Robine and Michel in looking forward to such a development and appreciate their first steps.
Acknowledgments
This work was funded by National Institute on Aging contract R01 AG021516.
The views expressed are those of the authors alone.
References
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