as one’s occupation. Since activities of daily living (e.g., dressing, bathing, and eating) are part of a set of expectations inherent in a variety of other social roles, Nagi sees deviations or limitations in the performance of even such basic social roles as components of the concept of disability (Nagi, 1991). For Nagi, disability as a heuristic concept is inclusive of all socially defined roles and tasks.

In the ICIDH-2, overall role performance mainly falls into the domain of participation. The boundary between activity limitation and participation is drawn differently from the way in which it is drawn in the Nagi model, in that a person who is unable to perform activities that are the components of roles is considered to have activity limitations (Figure 3). These are the roles that Nagi refers to as “basic social roles.” In the context of work disability, the distinction is between restriction of participation related to work as an overall concept and the carrying out of the activities involved in the work itself. This is discussed in more detail in the section that explores conceptual issues related to work disability.

Fundamental to differentiating the concept of disability from those of pathology, impairment, and functional limitation is the consideration of the difference between concepts of attributes or properties on the one hand and relational concepts on the other (Cohen, 1957).

As Nagi describes it:

Concepts of attributes and properties refer to the individual characteristics of an object or person, such as height, weight, or intelligence. Indicators of these concepts can all be found within the characteristics of the individual. Pathology, impairment, and functional limitations are concepts of attributes or properties…. Disability is a relational concept; its indicators include individuals’ capacities and limitations, in relation to role and task expectations, and the environmental conditions within which they are to be performed. (Nagi, 1991, p. 317)

Let us take the example of limitation in the performance of one’s work role—or work disability. Work disability typically begins with the onset of one or more health conditions that may limit the individual’s performance of specific tasks through which an individual would typically perform his or her job. The onset of a specific health condition—say, a stroke or a back injury—may or may not lead to actual limitation in performing the work role, a work disability. The development of work disability will depend, in part, on the extent to which the health condition limits the individual’s ability to perform specific tasks that are part of one’s occupation, and alternatively, degree of work disability may depend on external factors, for example, workplace attitudes—say, flexible working hours—that may restrict employment opportunities for persons with specific health-related limitations. Or work disability might be affected by



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