teachers, but also to other students, nurses, physicians, social workers, medical technicians, etc."

The point to be made is that components of roles—expectations, acts, actions, and tasks—are learned, organized, and purposeful patterns of behavior and not isolated muscle responses (Sarbin and Allen, 1968). Some acts, actions, and tasks are role specific, whereas others are common to the enactment of more than one role. Activities of daily living are learned, organized, and purposeful patterns of behavior. They are part of the set of expectations inherent in family, vocational, and a variety of other roles. Severe limitations in performing these tasks often result in reciprocal role relationships of dependency/assistance, which at times become contractual. The same reasoning applies to driving, the use of public transportation, the use of means of communication, and similar tasks, each of which separately does not constitute a social role but is part of many roles. Limitations in performing these tasks are components of the concept of disability.

The fifth issue concerning the disability framework relates to another criterion for differentiating the concept of disability from those of functional limitations, impairment, and pathology. For this, it will be useful to consider differences between concepts of attributes and properties on the one hand and relational concepts on the other (Cohen, 1957). Concepts of attributes and properties refer to the individual characteristics of an object or a 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 and properties. One need not go beyond examining a person to identify the presence and extent of physiological and anatomical losses or disorders, or to assess limitations in the functioning of the organism. In contrast, indicators of a relational concept cannot all be accounted for among the attributes of an individual. They include characteristics of other segments of the situation. 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.

The sixth and final issue is the question of whether disability, as conceptualized here, is limited to work. By now, it should be clear that the answer is no. Because of emphasis in public policy on concerns with dependence in economic and personal terms, and greater availability of support for studies of these dimensions, research developments were pushed largely in the direction of work disability and problems in independent living. However, the concept is inclusive of all socially defined roles and tasks. For heuristic purposes, Nagi (1969) applied a stress curve (Koos, 1954; Hill, 1958) to illustrate the processes of disability. As depicted in Figure A-1, the line between (a) and (b) represents the usual level of performance of an individual. The minor fluctuations are within the individual's margin of



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