Opportunities to Improve Survey Measures of Late-Life Disability: Part II - Workshop Summary. Measures of Environmentally Determined Mobility Disability


Dr. Shumway Cook presented an overview of her research on measures of environmentally determined mobility disability. She explained that although the exploration of the environment as a determinant of behavior is not new and the concept is especially important in models of the disablement process. According to the ICF, for example, environmental factors are external to the individual and interact with health conditions to produce barriers to full participation in society. In the Institute of Medicine’s publication “Enabling America” the disabling process occurs when the person’s need enlarge relative to the existing environment.

Dr. Cook’s research has focused on studying the environmental determinants of mobility disability in aging. Mobility is defined as the ability to move (walk) safely and independently in the environment. Mobility disability results from an interaction of the attributes of the individual (impairments and functional limitations) and attributes of the environment that constrain walking. In order to examine how attributes of the environment contribute to mobility disability in older adults, she developed with colleagues at the National Institute on Aging a model of the environment identifying features within the physical (natural or built) environment that affect the neural organization of a task related movement.

The model encompasses eight dimensions which represent the spectrum of external demand that have to be met for an individual to be fully mobile within a community context. These dimensions include: distance, temporal characteristics (the need to walk at a certain speed, as for example when crossing a street controlled by a traffic light), ambient conditions (light and weather conditions), terrain characteristics (both the geometry and surface features), physical load (including static loads such as when opening a heavy door, and dynamic loads such as when carrying packages that shift), attentional demands (walking while talking to a travel companion, navigating in an unfamiliar environment), postural transitions (having to stop, start, change directions, stoop, reach and turn), and density (number of people and object in the immediate environment requiring collision avoidance).

Using this model Shumway-Cook and colleagues developed a self-report survey, Environmental Analysis of Mobility Questionnaire (EAMQ), to determine the frequency with which specific features in the environment are encountered versus avoided during routine trips into the community. The instrument was pilot tested with 54 older adults (>70 years), who were recruited from two sites (Waterloo, Ontario, Canada and Seattle, Washington) grouped according to level of physical function (elite, physically able and physically disabled). The self-report survey examined 24 features of the physical environment, grouped into the eight dimensions. Older adults were asked, On routine trips into the community, how often do you encounter...." Each encounter question was paired with an avoidance question On routine trips into the community, how often do you avoid...." Frequency of encounter/avoidance was reported using a five-point ordinal scale (never, rarely, sometimes, often, always). Frequency of encounter/avoidance was determined for each individual dimension, and in addition, a total encounter and avoidance score was calculated by summing across dimensions.

Results from the survey pilot study suggested that mobility disability was associated with reduced encounter and increased avoidance of physical features within the environment that impacted walking. However, not all features of the environment were avoided, instead both encounter and avoidance varied by environmental dimensions. Results supported the concept that mobility disability results from an interaction between the individual and the environment. Furthermore, it suggested that some features within the environment were more disabling to mobility than others.

Further research has begun to test the psychometric properties of the EAMQ. To test the reliability of the survey, older adults completed the survey twice, one week apart. The test-retest reliability was good (ICC = 0.81-1.0). The validity of the EAMQ was examined in several ways. Dr. Shumway-Cook and colleagues compared self-report responses to observed behavior in the community, and to level of ADL and IADL disability. As a part of the pilot study older adults were directly observed during six trips into the community to perform activities of daily life (grocery shopping, visit to medical practitioner, social participation, etc.). Frequency of encounters with environmental features within each of the eight dimensions was recorded. Results from the direct observation protocol identified environmental demands associated with mobility in the community. In addition, similar to the survey results, the direct observation study found that mobility disability was not associated with a uniform decrease in encounters across all dimensions, rather certain dimensions were encountered less frequently by the disabled compared to nondisabled, while features in other dimensions showed comparable levels of encounters among the groups. Results from the direct observation protocol supported the survey results in suggesting that certain environmental features may be more disabling than others to community mobility.

In summary, as a survey tool, the EAMQ has a number of strengths. It appears to be a reliable way to determine perceptions related to features within the environment that disable community mobility. It has demonstrated concurrent validity with community mobility directly observed, and is strongly associated with disability in activities of daily life. Current limitations of this survey are its length and the redundancy of questions within each dimension. In addition, it has been tested on only a small sample of older adults, and therefore requires further testing.

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