The Concept of Disability

Disability itself is not always quantifiable. In the Americans with Disabilities Act of 1990 an individual with a disability is defined as a person who has a physical or mental impairment that substantially limits one or more major life activities.⁴⁰ The concept of disability differs among persons who consider themselves to have a disability, professionals who study disability, and the general public.²² This lack of agreement is an obstacle to all studies of disability, as well as to the equitable and effective administration of programs and policies intended for people with disabilities.^{12,13,22,28,30}

The World Health Organization (WHO) has a mandate to develop a global common health language—one that is understood to include physical, mental, and social well-being. The International Classification of Impairments, Disabilities, and Handicaps (ICIDH-2) was developed by WHO as a tool for classification of the “consequences of disease.” The ICIDH-2 reflects the biopsychosocial model of disablement, viewing disablement and functioning as outcomes of an interaction between a person’s physical or mental condition and the social and physical environment. Human functioning is characterized at three levels: the body or body part, the whole person, and the whole person in social context. Disablements are the dimensions of dysfunctioning that result for an individual at these three levels; these include impairment, losses, or abnormalities of bodily function and structure; limitations of activities; and restrictions of participation.

This biopsychosocial model regards functioning and disablement as outcomes of interactions between health conditions (disorders or diseases) and conceptual factors such as social and physical environmental factors and personal factors. The interactions in this paradigm are dynamic, complex, and bidirectional (Figure 35-1).

FIGURE 35-1 Biopsychosocial model of disablement.

Dimensions of dysfunctioning are defined as follows.

The concept of disability or disablement continues to be one about which there are many interpretations and opinions. This lack of agreement about the concept of disablement affects epidemiologic studies of disablement and the development of effective treatment and prevention strategies. The biopsychosocial model and the common language of the ICIDH-2 helped to define the need for health care and related services; define health outcomes in terms of body, person, and social functioning; provide a common framework for research, clinical work, and social policy; ensure the cost-effective provision and management of health care and related services; and characterize physical, mental, social, economic, and environmental interventions that would improve lives and levels of functioning.⁵¹

The 2001 World Health Assembly subsequently endorsed a revised system, the International Classification of Functioning, Disability and Health (ICF). This is a classification of health and health-related domains, which are classified from body, individual, and societal perspectives using a list of body functions and structure, as well as a list of domains of activity and participation. The ICF also includes a list of environmental factors to provide context for the disability.⁵³ The ICF provides a common transcultural language across health care systems and is intended to allow comparison of international data and the measurement of health outcomes, quality, and cost, as well as health disparities.

Data: Impairment and Disability

The U.S. Census Bureau provides extensive information on the number and characteristics of people with disabilities. Data from the Americans with Disabilities Report of 2005 indicate that 54.4 million people, or 18.7% of the U.S. population,⁴⁰ have some level of disability. Among those 15 years or older, inability to walk without an assistive device was reported by 10.2 million individuals, and 3.3 million individuals required a wheelchair. Requiring help with one or more activities of daily living was reported by 4.1 million.⁴⁰

Impairments resulting from chronic disease have become increasingly significant risk factors of disability.^8,22 Table 35-1 lists the 15 conditions with the highest prevalence of functional compromise or disability.²² The prevalence of disability with these conditions appears to be due to the prevalence of the condition itself and the chance that the condition will cause a disability. Table 35-2 shows the ranking of persons, by percentage of specific conditions, who have functional limitations secondary to that condition.²² In general, many of the conditions that are significant risk factors for disability are low in prevalence. For example, multiple sclerosis has a low overall prevalence but is a significant risk factor for disability. Examination of this ranking shows 7 of the top 10 disabling conditions are conditions frequently managed by the physiatrist and the rehabilitation team. These conditions or diseases are typically chronic, requiring a lifetime of rehabilitative management to have an effect on the disabling process, prevent secondary conditions, and maintain quality of life.

Table 35-1 Conditions With the Highest Prevalence of Activity Limitation

From La Plante MP: The demographics of disability, Milbank Q 69:55-77, 1991, with permission.

Socioeconomic Effect of Disability

Disablement has significant socioeconomic consequences for the individual with disabilities and for society. When a person is unable to participate in her or his social role as a worker or homemaker because of a physical or mental condition, that person is said to have a work disability or a work participation restriction.^7,54 Work participation restriction results in dependency and loss of productivity for that person. Society, in turn, incurs direct and indirect costs.

Direct expenditures include those for medical and personal care, architectural modification, assistive technology, and institutional care, as well as income support for the person with a disability. For the individual, these expenses contribute to impoverishment.^6,49 Society’s response to the expenditures related to disablement includes disability-related programs such as Social Security Disability Insurance (SSDI), Supplemental Security Income (SSI), Medicare, and Medicaid. In 2002, federal and federal–state programs for working-aged people with disabilities were estimated to cost $276 billion, or 2.7% of the gross domestic product (GDP) of the United States.¹¹

Disablement is costly to the individual and to society because of the loss of productivity. People with disabilities are more likely to be unemployed or underemployed and have lower average salaries than their nondisabled peers (Table 35-3). The indirect monetary costs for the individual are reckoned in terms of losses in earnings and homemaker services.⁵⁵ A 2006 study by researchers at the University of California, using 1997 as an example year, found that people with disabilities were estimated to spend an average of 4.5 times as much on medical expenses⁵⁵ and that the overall net salary loss associated with disability was $115.3 billion, or 1.4% of the 1997 GDP.⁵⁵

Disablement is associated with poverty. In 2007, 21% of disabled people 5 years and older were below the poverty level as opposed to only 10.9% of those without a disability.⁴¹ In 2005, people 21 to 64 years of age without a disability had median monthly earnings of $2539. Those with a nonsevere disability had $2250 median monthly earnings, and those with a severe disability had $1458 median monthly earnings (Table 35-3).⁴⁰ The indirect monetary cost to society is loss from the labor force.⁶ For example, in 1996, spinal cord injury alone was estimated to have cost the U.S. economy $9.73 billion, including $2.6 billion in lost productivity.²⁴

Disablement imposes indirect nonmonetary costs to the individual and to society. Fifty-seven percent of persons with disabilities believed their disability prevented them from reaching their full potential.¹⁴ Restriction in work participation, in particular, places the individual in a position of dependency on insurance payments or government benefits for income support and medical care. Dependency affects people’s feelings about themselves and their overall satisfaction with life.

Pressure from various customers, and especially the third-party payers, for accountability in medical care focuses attention on outcome and cost-effectiveness. Interventions directed at disablement should be assessed with measures of both outcome and cost-effectiveness. Disablement is more than a medical phenomenon: It is a complex socioeconomic process. Assessment of the outcome and cost-effectiveness of an intervention should take into consideration the quality of life and indirect monetary costs, as well as direct expenditures.

Vocational rehabilitation is an intervention that can limit restrictions in work participation. In 1993, the Social Security Administration estimated that for every dollar spent on vocational rehabilitation services, five dollars in future direct expenditures was saved.²³ A 2006 analysis of spending by the New Mexico Division of Vocational Rehabilitation found a total benefit/cost ratio of 5.63.²⁹ Although employment is the expected outcome of vocational rehabilitation, the impact of this intervention goes beyond simple employment and saving of direct expenditures. The positive effects of working are demonstrated when the characteristics of working and nonworking persons with disabilities are compared. Those who work are better educated, have more money, are less likely to consider themselves disabled, and in general are more satisfied with life.¹⁴

Comprehensive rehabilitation of persons with disabilities should include strategies that reduce work restrictions, such as vocational rehabilitation. The outcomes include increased independence and increased productivity. The cost-effectiveness of comprehensive rehabilitation should be measured in direct and indirect monetary and nonmonetary costs over the lifetime of the individual.³

Disability-Related Programs and Policies

Vocational Rehabilitation