The Role of the Built Environment and Assistive Devices for Outdoor Mobility in Later Life

Since the Institute of Medicine’s milestone report on Disability in America (Pope & Tarlov, 1991), disablement models have conceptualized disability as a process, with the aim of better understanding how to prevent potentially disabling conditions from developing into disabilities. (Nagi, 1965; Verbrugge & Jette, 1994; World Health Organization, 2001) For example, the WHO’s International Classification of Functioning Disability and Health (known as the ICF [World Health Organization, 2001]) conceptualizes disability as an umbrella term that captures the consequences of disease at three levels (Figure 1): (a) at the level of the body, impairments in body functions and structures; (b) at the level of the person, restrictions in everyday activities; and (c) at the level of society, participation in life situations and social roles (Jette & Badley, 2000). Figure 1. Conceptual model: the dynamic nature of disability (adapted from WHO 2001). There is also recognition of the dynamic and contingent nature of the disablement process. Current models of disability (Verbrugge & Jette, 1994; World Health Organization, 2001) have drawn attention to environmental factors that can interact with underlying impairments to impede or enhance a person’s ability to carry out activities (dashed arrow in Figure 1). There are multiple types of environmental factors that can either serve as barriers or facilitators to independence for people with underlying health conditions (Srinivasan, O’Fallon, & Dearry, 2003). The ICF identifies products and technology (e.g., mobility devices), services and policies, attitudes, supports and relationships, as well as natural and human-made built environments (World Health Organization, 2001). For example, following a stroke an individual may experience hemiparesis (impairments in body functions and structures) that leads to severe difficulty in walking a quarter mile (mobility restriction), which then restricts his or her involvement in life situations, such as meeting with neighbors or close friends (participation restriction). But living on a street with continuous, barrier-free sidewalks may facilitate outdoor mobility, with positive consequences for his/her ability to visit with friends down the street (participation). Motivated in part by these conceptual models, researchers have begun to examine the role of the environment in the disablement process by focusing on the modifying effect of the urban-built environment in the pathway between impairments and outdoor mobility (Clarke & George, 2005; Michael, Beard, Choi, Farquhar, & Carlson, 2006; Clarke, Ailshire, Bader, Morenoff, & House, 2008; Freedman, Grafova, Schoeni, & Rogowski, 2008; Clarke, Ailshire, & Lantz, 2009; Clarke, Ailshire, Nieuwenhuijsen, & de Kleijn-de Vrankrijker, 2011). Results indicate that uneven sidewalks and sidewalk obstacles (i.e., loose stones and other debris) are responsible for the vast majority of outdoor falls among older adults (Berg, Alessio Mills, & Tong, 1997; Li et al., 2006) and poor street and sidewalk conditions are associated with fourfold higher odds of mobility difficulty among older adults with underlying lower extremity weakness (Clarke et al., 2008). Moreover, compared with functionally independent older adults, older adults with lower extremity impairment avoid grassy terrain or terrain with other obstacles (Shumway-Cook et al., 2002, 2003). These findings highlight the importance of considering not only an individual’s physical capacity but also the demands created by the environment (person–environment fit), as they jointly influence independent mobility (Lawton, 1985; Balfour & Kaplan, 2002; Iwarsson, Horstmann, Carlsson, Oswald, & Wahl, 2009). Yet, despite theoretical advances in our conceptualization of disability, the “environment” remains a largely unspecified term in disablement models. With respect to mobility disability, we do not know which particular environmental features matter most and for whom. Do environmental factors matter more for people with lower levels of functional capacity (impairment in ICF terms), and less so for people without any impairments? Mobility devices (e.g., cane, walker, wheelchair) also fall under the rubric of “environmental factors” in conceptual models. Yet we know very little about which ones are the most important facilitators for mobility and how they interact with other built environment features. For example, people who use wheeled mobility devices rely heavily on ramps and curb cuts for outdoor mobility. But for someone using a cane, curb cuts may not be as important. In addition, research to date has not differentiated between older adults residing in single family homes and multi-unit apartment buildings. Are outdoor built environment features less important for those in multi-unit dwellings where factors located inside the building are more likely to influence the level of difficulty going outside? Finally, for how many people does the environment play a role in mobility? To date, a lack of nationally representative data on these concepts has prevented us from quantifying the potential impact of particular environmental features on mobility in older Americans. The purpose of this research is to draw on data from the first round of the National Health and Aging Trends Study (NHATS) to tease apart and specify the complex role of the environment in the disablement process (Freedman et al., 2011). Funded by the National Institute on Aging, NHATS is an annual, nationally representative study of Americans age 65 and older, with the first wave conducted in 2011. NHATS provides a unique opportunity to disentangle the role of individual and environmental factors in the disablement process due to a rigorous disability measurement protocol that seeks to disaggregate measures of activity limitations into impairments (using performance-based assessments of physical capacity), compensatory strategies, and environmental factors. For example, rather than simply asking respondents about difficulty with outdoor mobility, NHATS first asks how often they use a cane, walker, wheelchair, or scooter for outdoor mobility. Then, respondents are specifically asked how much difficulty they have with outdoor mobility when using that particular device. In addition, NHATS also collects standardized data on each respondent’s home and outdoor environment using interviewer observations. Thus, the NHATS framework provides a unique opportunity to distinguish between the role of assistive devices (accommodations) and the environment in outdoor mobility disability.