Nagi’s definition stipulates that a disability may or may not result from the interaction of an individual’s physical or mental limitations with the social and physical factors in the individual’s environment. Consistent with Nagi’s concept of disability, an individual’s physical and mental limitations would not invariably lead to work disability. Not all physical or mental conditions would precipitate a work disability, and similar patterns of work disability may result from different types of health conditions. Furthermore, identical physical and mental limitations may result in different patterns of work disability.
Nagi’s Disablement Model has its origins in Functionalism identified most closely with Talcott Parsons (1951). In the early 1960s, as part of a study of decision making in the SSDI program, Nagi (1964) constructed a framework that differentiated from three other distinct yet interrelated concepts: active pathology, impairment, and functional limitation. This conceptual framework has come to be referred to as Nagi’s Disablement Model.
In their work on the disablement process, Verbrugge and Jette (1994) maintained the basic Nagi concepts and his original definitions. Within the dimension of disability however, they categorized subdimensions of social roles that can be considered under Nagi’s concept of disability. Some of the most commonly applied dimensions include activities of daily living, instrumental activities of daily living, paid and unpaid role activities, social activities, and leisure activities. Within their framework, work disability is clearly delineated as a specific subdimension under the concept of disability.
A further elaboration of Nagi’s conceptual view of the term disability is contained in Disability in America (IOM, 1991) and in a more recent IOM revision of the disablement model highlighted in a report titled Enabling America: Assessing The Role of Rehabilitation Science and Engineering (IOM, 1997b). The 1991 IOM report uses the original main disablement pathways put forth by Nagi with minor modification of his original definitions. That report makes two important additions to the Disablement Model: the concepts of “secondary conditions” and “quality of life.” In 1997, in an effort to emphasize that disability is not inherent in the individual (as defined by SSA) but rather is a product of the interaction of the individual with the environment, the IOM issued the second report, Enabling America, where it referred to disablement as “the enabling–disabling process.” This effort was an explicit attempt to acknowledge within the disablement framework itself that disabling conditions not only develop and progress but can be reversed through the application of rehabilitation and other forms of explicit intervention.
The ICIDH, now revised and renamed the International Classification of Functioning, Disability and Health (WHO, 2001), has moved away