Disablement, Models of

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Disablement, Models of


Models of disablement refers to systems of definitions and theories about human disability that are used to provide a framework for discussion or to explain disabilities in relation to clinical diagnosis, rehabilitation medicine, employment issues, public policy-making, and similar concerns. As of the early 2000s, there are two major models of disablement used in English-speaking countries: the Nagi model, derived from the work of Saad Nagi, a professor emeritus of sociology who taught at Ohio State University; and the World Health Organization (WHO) model, which underwent two major stages of drafting and revision in 1980 and 2002 respectively. While the Nagi model was not accompanied by an attempt to classify human disabilities, both versions of the WHO model were intended to supplement a parent document, WHO's International Classification of Diseases or ICD. The earlier version of the WHO model of disablement was called the International Classification of Impairment, Disability and Handicap, or ICIDH, while the newer document (originally called ICIDH-2), was published as the International Classification of Functioning, Disability and Health, abbreviated as ICF.


Disability statistics

The significance of models of disablement for decisions about medical treatment and rehabilitation as well as government policy is underscored by the sheer size of the disabled population in the United States alone. A National Health Interview Survey (NHIS) taken in 1994 estimated that 15 percent of the civilian population outside of nursing homes or other institutions—38 million people—suffered from limitations on their activity caused by chronic health problems. The Institute of Medicine (IOM) grouped this population into the following categories of disablement: limitations on mobility, 38 percent; chronic disease, 32 percent; limitations of sight or hearing, 8 percent; intellectual limitations, 7 percent; and other conditions, 15 percent. In addition to the NHIS data, a 1996 Survey of Income and Program Participation (SIPP) reported that 48.9 million Americans were limited in performing certain functions or fulfilling their socially defined role or task. With regard to activities of daily life (ADLs), such as shopping, managing money, and housekeeping chores, 8 million Americans were identified in a 1993 study as having some difficulties with them, while half of this group, or 4 million persons, needed the assistance of another person. The annual disabilities-related cost to the United States is over $200 billion.


All theoretical models of disablement are products of the twentieth century. They developed as the medical advances in the early part of the century shifted the focus away from treating acute infectious diseases that had previously killed large numbers of people (such as smallpox, diphtheria, and typhoid fever) toward an emphasis on treating chronic conditions, including disabilities of various types. In addition, the growth of social welfare programs during and after the New Deal of the 1930s made it necessary to define and classify disabilities in order to determine people's eligibility for worker's compensation and other government health care benefits. A third factor was the passage (in the United States) of several vocational rehabilitation acts by Congress in the 1940s and 1950s, which led to the rapid growth, not only of hospital clinics and other centers for rehabilitation, but also the number of helping professions that became involved in rehabilitation. These professions included education, psychology, social work, psychotherapy, and occupational therapy as well as medicine and nursing.

By the 1950s, the importance of standardizing definitions and measurements of disability had become obvious to most observers. Some researchers worked on the development of scales for measuring a person's ability to perform so-called activities of daily life, or ADLs. In 1958 the American Medical Association (AMA) formed a Committee on Medical Rating of Mental and Physical Impairment to draft a set of standardized ratings to measure the type and extent of a person's disability. This so-called medical model of disablement was primarily concerned with functional assessment of patients; that is, its measurements focused on limitations—specifically, the patients' loss of ability to carry out certain actions or activities, especially those related to employment.

The medical model of disablement has been criticized since the 1950s, however, for several reasons:

  • It tends to define disablement as the individual patient's problem, to be treated by medical intervention or correction.
  • It focuses on the person's ability to attend school or hold a job rather than on other aspects of his or her involvement in a family or the larger society.
  • It tends to emphasize treatment of existing disabilities rather than prevention of future health problems.
  • It tends to regard disabilities as permanent conditions, when in fact some are temporary or intermittent, such as depression or other emotional disorders.
  • It defines disablement largely in negative terms, as the loss of or limitations on functioning.

The Nagi model

Saad Nagi is a sociologist who originated a model of disablement that broke new ground by redefining disability as a gap between a person's physical, intellectual, or emotional capabilities and the demands of that person's physical or social environment. In Nagi's own words, "disability is the expression of a physical or a mental limitation in a social context." Nagi drew up a framework of four interrelated ideas in the early 1960s as part of a large-scale study for the Social Security Disability Insurance (SSDI) program. His four ideas or concepts are as follows:

  • Active pathology. Nagi defined active pathology as any interruption of or interference with a person's bodily processes or structures. Active pathology may result from contagious disease, trauma, inherited defects or disorders, extremes of heat or cold, chemical agents, or other causes.
  • Impairment. Impairment according to Nagi is any loss or abnormality of any physical, mental, emotional, or physiological structure or function. Impairments are related to specific organs or organ systems, but not to the person as a whole.
  • Functional limitations. Nagi used this term to refer to the effects of impairments on the person's performance capacity as a whole. All functional limitations are caused by impairments, but not all impairments result in functional limitations. For example, two people may have the same degree of impaired range of motion in the fingers due to arthritis, but one may be able to play a keyboard instrument while the other cannot, if the first person has a higher threshold of pain. Another example of an impairment that does not cause functional limitation is nearsightedness (a visual impairment), which does not limit a person's activity provided he or she wears corrective lenses.
  • Disability. This last concept refers to the person's social functioning. It can be defined as an inability to perform certain activities within socially defined roles and tasks, such as work, education, family relationships, self-care, and recreation. The importance of this social definition of disability is that it helps to explain why two persons with the same type of impairment and functional limitations may have very different patterns of disability. Nagi noted three sets of factors that shape or influence a given person's pattern of disability: 1) the person's reaction to his or her situation; 2) the way others (family members, teachers, employers, etc.) define and react to the person's disabling condition; and 3) the person's environment, which may present physical or cultural barriers to the disabled person. To give a specific example, one child with cerebral palsy may be encouraged by parents and teachers, and attend school in a setting that accommodates his slow movements and awkward gait, while another child with the same disorder may become depressed because of his family's disapproval or feelings of shame, and may not be able to go to a school for students with special needs. The two children will develop very different patterns of disability even though they were diagnosed with the same disorder.

Nagi's four concepts served as the basis for the models of disablement developed by several major research centers and government agencies in the United States in the 1990s. Nagi's original model was first presented to the wider health care community in an important report, Disability in America, published by the Institute of Medicine (IOM) in 1991. In 1997 the IOM published a second book, Enabling America, which expands Nagi's model with a fuller description of the environment that surrounds a disabled person. The environment is now understood to include the economic system, culture, political system, and psychological factors as well as the natural and the humanly constructed environment.

In addition, the 1997 publication explicitly defined disablement as a process rather than an event or static condition. It spoke of "the enabling-disabling process" to explain not only that Nagi's four concepts can be understood as stages in the development of a disabling condition, but also to point out that disabilities can be reversed through rehabilitation and other interventions. For example, a person may notice the first signs of osteoarthritis (active pathology) in the knee joints in midlife. As the joints continue to deteriorate, the person may suffer from pain and loss of flexibility in the knees (impairment). If the arthritis is not treated, the person may have to restrict such activities as running or playing tennis, and may find walking or climbing stairs increasingly difficult (functional limitation). Eventually the person may have to ask family members for help with certain chores or activities, move to a house or apartment without stairs, or even change employment (disability). This progression can be reversed, however, by an enabling process that either restores the person's function, gives them easier access to the environment, or both. In the specific example just given, the enabling process might include such treatments as medications to relieve pain in the knees, exercises to maintain strength and flexibility in the knees, surgical replacement of the affected joint with an artificial knee, the use of walkers or similar assistive devices, or redesigning the person's workplace to allow for their difficulty in walking or standing for long periods of time.

The Nagi model was also adopted but slightly modified by the National Center for Medical Rehabilitation Research (NCMRR), which was established by the National Institutes of Health (NIH) in 1990 as part of the National Institute of Child Health and Human Development (NICHD). The NCMRR added a fifth aspect of human functioning, societal limitation, to Nagi's original four.

Nagi's model of disablement was also supplemented in 1994 by a landmark article by Lois Verbrugge and Alan Jette on the process of disablement. The authors suggested analyzing Nagi's outline of the process with regard to three sets of factors, which they termed risk factors, intraindividual factors, and extraindividual factors:

  • Risk factors. These are present before the onset of the active pathology and may affect the severity or speed of the disablement process. They include socioeconomic status (SES), genetic traits, and lifestyle.
  • Intraindividual factors. These operate inside the person, and include such factors as behavioral changes (such as quitting smoking or losing weight), psychological characteristics, coping skills, and stress hardiness.
  • Extraindividual factors. These include the physical environment and such features of the person's social environment as medical or psychiatric treatment, rehabilitation services, medications, assistive devices, and family and friendship networks.

The WHO model

The WHO model of disablement originated from a different set of concerns than the Nagi model. Whereas Nagi was attempting to construct a model for a government benefit program, WHO was interested in devising a system that could be used to collect and standardize medical data from many different countries. The first version of the WHO model, the ICIDH, was described as a "manual of classification relating to the consequences of disease" because the system used in developing WHO's International Classification of Diseases (ICD) did not work well when applied to impairments and disabilities. Dr. Philip H. N. Wood, a physician who specialized in the treatment of arthritis and other rheumatic diseases, outlined four concepts related to disablement in the introduction that he wrote for the document that WHO published in 1980:

  • Disease. Wood defined disease as "something abnormal occur[ring] within the individual."
  • Impairment. For Wood, impairment takes place when the individual becomes aware of the disease; in his words, "the pathological state is exteriorized."
  • Disability. Wood defined disabilities as "disturbances at the level of the person…. [A] disability is any restriction or lack (resulting from impairment) of ability to perform an activity in the manner or within the range considered normal for a human being."
  • Handicap. To Wood, a handicap represents the "socialization" of a disability; that is, a handicap places the person at a social disadvantage and "limits or prevents the fulfillment of a role that is normal" for that person.

The reader will notice at once that Nagi and Wood used the same terms in different ways, which led to considerable confusion among their readers. Wood's "handicap" is roughly equivalent to Nagi's "disability," while Wood's "disability" is similar to Nagi's "functional limitations." In addition, Wood's retention of the term "handicap" touched off an international controversy among health care professionals and advocates for the disabled, who pointed out that the word had been used in the past to stigmatize people with disabilities.

When WHO proposed to revise the ICIDH in the late 1990s, the original questioning of the term "handicap" was extended to the entire classification scheme. A number of experts remarked that the ICIDH tended to emphasize deficiencies, and they urged the revision committee to use more neutral language. As a result, the ICF (or ICIDH-2) that was published in 2002 replaced "disability" with "difficulty with activity," and "handicap" with "limitations on participation" in educational, employment-related, or social activities. In general, the ICF prefers the phrase "level of health" or "health condition" to "disease" or "disability." It thus "'mainstreams' the experience of disability and recognizes it as a universal human experience."


One controversy that has developed with regard to models of disablement is whether disabled persons should be defined as a minority group for purposes of political action. This controversy has affected public policy in Europe as well as in Canada and the United States. Some observers maintain that disabled persons have been victims of social prejudice and workplace discrimination in the same way as members of racial and ethnic minority groups, and that they should therefore seek change through civil rights legislation. Other researchers maintain that a universalist approach to legislative and other changes is more beneficial to the disabled, for two reasons. One is that disabilities vary so widely in terms of their severity and their specific effects on normal human functioning that it is difficult to categorize "the disabled" as a single or unified minority group. The ICF maintains that "a classification of functioning and disability should be applicable to all people … [and] not become a tool for labeling persons with disabilities as a separate group." A second consideration is the growing recognition of the complexity of the enabling-disabling process as defined by the IOM in 1997. Not only are some disabilities easier to treat or reverse than others, but also the risk factors and intraindividual differences that contribute to the pattern of an individual disability can combine in a nearly infinite number of ways. Furthermore, if prevention of future disablement is added to public policy deliberations, "the disabled" is no longer a minority group but includes most of the adult population.

The concept of an "emerging universe of disability," in which the distribution of disability in the general population will change, along with increases in the frequency of certain types of impairments and changes in the consequences of disability, has gained support among some researchers. One factor that is frequently mentioned is the lengthening of the life-span in developed countries, and an associated rise in impairments and disabilities related to aging—such as limitations on mobility or the mental limitations resulting from Alzheimer's disease. As of the early 2000s, a newborn with a life expectancy of 75 years can expect to spend 13 of those years with one or more limitations on his or her activity. Another set of factors, sometimes called the "new morbidity," concerns such conditions associated with poverty as inadequate education and medical care, substance abuse, environmental hazards, and interpersonal violence. All of these conditions are associated with higher rates of impairments and disabilities. A third factor is the emergence of new diseases or disorders, such as AIDS, chronic fatigue syndrome, or repetitive stress injuries, that lead to various impairments or disabilities.


Assistive device— Any item or piece of equipment that is designed or modified to improve, maintain, or restore the functioning of persons with disabilities.

Model— A system of concepts or hypotheses used to explain a phenomenon. Models of disablement are systems of definitions and theories about human disability used to relate it to diseases and other medical disorders, rehabilitation, social and political systems, and similar concerns.

Stigma— A mark or sign of shame or reproach. Models of disablement are presently used to remove the stigma historically associated with disabilities, among their other purposes.

Universalism— The notion that definitions leading to public policy changes should apply to everyone rather than to special interest groups.

Professional implications

Both the Nagi and the WHO models of disablement have a number of implications for health care professionals:

  • Professional education and training. As of the early 2000s, these models are used in classroom instruction for physical therapists, social workers, clinical psychologists, and psychotherapists as well as nursing and medical students.
  • Clinical evaluation of patients. Models of disablement are presently used to help orthopaedic surgeons, gerontologists, neurologists, and other specialists decide on the most helpful interventions for patients with disabilities. In particular, evaluations of elderly patients in North America often make use of the Nagi model in determining a specific patient's need for personal assistance or nursing home care.
  • Public health research. As was mentioned previously, the ICF was explicitly designed to facilitate data collection and analysis related to disablement issues. Changing patterns in the distribution of specific disabilities and the emergence of new types of disabilities can be tracked more effectively with the help of these theoretical models. In addition, models of disablement help to standardize data collected for outcome studies intended to measure or compare treatments and interventions.
  • Technological inventions and innovations. The new emphasis on the rehabilitation and social reintegration of persons with disabilities has stimulated engineers, medical experts, and designers to pool their resources and look for ways to help people overcome environmental barriers. Such inventions as voice-operated computer systems, battery-powered scooters for persons with mobility impairments, cell phones for people with visual or hearing losses, and cars modified for use by persons with hand or leg impairments are only a few of the ways in which modern technology is being put to work. Japan in particular is a pioneer in this field.
  • Public policy development. Models of disablement are useful in guiding legislative definitions of disability that can be used in turn to determine a person's eligibility for disability pensions, to mandate the construction of accessible housing, to set up special schools for students with disabilities, and similar concerns.



Brandt, Edward N., Jr., and Andrew M. Pope, eds. Enabling America: Assessing the Role of Rehabilitation Science and Engineering. Washington, DC: National Academy Press, 1997.

Goffman, Erving. Stigma: Notes on the Management of Spoiled Identity. New York: Simon and Schuster, 1986. First published in 1963, this now-classic book was one of the first explorations of the social barriers caused by disabilities of various types, psychiatric as well as medical.

Jette, Alan M., and Elizabeth Badley. "Conceptual Issues in the Measurement of Work Disability." Chapter 2 in Nancy Mathiowetz and Gooloo S. Wunderlich, eds., Survey Measurement of Work Disability: Summary of a Workshop. Washington, DC: National Academy Press, 2000.

Pope, Andrew M., and Alvin R. Tarlov, eds. Disability in America: Toward a National Agenda for Prevention. Washington, DC: National Academy Press, 1991.


Bickenbach, J. E., S. Chatterji, E. M. Badley, and T. B. Üstün. "Models of Disablement, Universalism, and the International Classification of Impairments, Disabilities and Handicaps." Social Science and Medicine 48 (May 1999): 1173-1187.

Thomas, Gerald. "Tokyo Motor Show." New Mobility (March 2005).

Verbrugge, L. M., and A. M. Jette. "The Disablement Process." Social Science and Medicine 38 (January 1994): 1-14. This article has become a classic in the field of disability studies and research.

Wood, P. H. N. "Applications of the International Classification of Diseases." World Health Statistics Quarterly 43 (1990): 263-268.


Institute of Medicine (IOM). 500 Fifth Street, NW, Washington, DC 20001. (202) 334-2352. Fax: (202) 334-1412. 〈http://www.iom.edu〉.

National Institute of Child Health and Human Development (NICHD), National Center for Medical Rehabilitation Research (NCMRR). Executive Building, Room 2A03, 6100 Executive Blvd., MSC 7510,

National Institute on Disability and Rehabilitation Research (NIDRR). U. S. Department of Education, 400 Maryland Avenue, SW, Washington, DC 20202-2572. (202) 245-7640. Fax: (202) 245-7323. 〈http://www.ed.gov/about/offices/list/osers/nidrr〉.

World Health Organization (WHO): International Classification of Functioning, Disability and Health. Contact: T. B. & Uuml;stün. 20, Avenue Appia, 1211 Geneva, Switzerland. E-mail: [email protected]. 〈http://www3.who.int/icf〉.


Nagi, Saad Z. "Disability Concepts Revisited: Implications for Prevention." Published as Appendix A to Disability in America: Toward a National Agenda for Prevention. Washington, DC: National Academies Press, 1991.

Taubes, Gary. "An Interview with Lois M. Verbrugge, Ph.D., MPH." In-Cites, June 2003. 〈http://www.in-cites.com/papers/DrLoisVerbrugge.html〉.

World Health Organization (WHO). Towards a Common Language for Functioning, Disability and Health: ICF. Geneva, Switzerland: WHO, 2002.

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