American Journal of Preventive Medicine
Research articleAssessing the building blocks of function: Utilizing measures of functional limitation
Introduction
O ne of the hallmarks of clinical geriatric practice and gerontologic research is the orientation to older people's ability to function and the disablement process. The approach adds an additional dimension beyond the usual medical assessment, providing information on well-being and quality of life as well as determining care needs and prognosis. Functional status and disability reflect both the negative and positive aspects of health status and offer a way of summarizing the balance between the negative impact of multiple medical conditions of varying severity and the overall health and vitality of the individual.
A wide array of measures that tap into the disablement process have been employed in the assessment of older people. The earliest assessments were aimed at evaluating basic self-care ability, with assessments of ability to remain independent in the community following soon thereafter. In the past 2 decades, many more assessment tools have been developed for a wide array of uses. These instruments, which have included both self-report batteries as well as objective, standardized tests of performance, have added to our understanding of the disablement process in the older population. What has been lacking, however, has been a unifying scheme that allows us to organize and categorize these instruments in a way that may improve our understanding of what different tools are truly measuring and how the measures that these tools provide relate to each other.
A very basic approach is to classify measures that track different stages along the disablement pathway according to whether they identify functional limitations, the focus of this article, or disability. While these categories are related to each other, they represent very different concepts. Discriminating our current instruments and developing future instruments with this distinction in mind will help to clarify many of the conceptual and practical challenges in this important mode of assessing older people.
Section snippets
Defining a functional limitation
According to the original classification scheme proposed by Nagi,1 functional limitations are defined as “limitations in performance at the level of the whole organism or person.” By contrast, disability is defined as “limitation in performance of socially defined roles and tasks within a sociocultural and physical environment.” An important advantage of utilizing different definitions for functional limitations and disabilities, as originally proposed by Nagi, is that they can be envisioned as
Tools used to measure functional limitations
In the past 15 years, objective measures of physical performance have been promoted as a useful measurement tool in the assessment of physical function.7 When first employed, physical performance measures were simply seen as another way of assessing disability, but with the added benefit of being objective and standardized. As the Nagi pathway was recognized as being a useful framework to organize our approach to the disablement process, it became clear that most performance measures were not
The value of employing functional limitations as outcomes
There are a variety of advantages to employing functional limitation measures in clinical and epidemiologic studies of older populations. In evaluating the consequences of disease and impairment, it is relevant to assess how these factors cause disability. However, using functional limitations as more proximal outcome measures can add clarity to the relationships under investigation. A key reason for this is that they represent an outcome that is free of the variable environmental influences
Using functional limitations as predictors
Measures of functional limitation have been shown to classify subjects across a wide range of function. For example, early work with the EPESE battery showed that when the population was stratified into three disability subgroups, one with ADL disability, one with no ADL disability but disability in mobility, and one with no disability, there was a distribution of performance within each subset, with the distributions shifted to the low, middle, and high end of the scale, respectively.13 This
Challenges in the assessment of functional limitations
During the 1990s, there was substantial progress in the assessment of function in older populations due to both the clarification of the concept of functional limitations and the development and use of specific measures of functional limitation in a variety of research settings. Although the field has now reached a relatively mature state, there are still many areas in which further progress would be very valuable. A summary of four key areas that require more attention is presented in Table 4.
Conclusion
Assessing functional limitations may add valuable information in both the research and clinical settings. The framework for tracking the progression from disease to disability is now well established, and initial research that explores the transitions along this pathway has been highly instructive. Functional limitations are a critical step in the pathway and work well to demonstrate the impact of disease and impairments on functioning, characterize the functional abilities of individuals or
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