Conceptual Issues in the Measurement of Work Disability
Alan M. Jette
Boston University’s Sargent College of Health and Rehabilitation Sciences
Arthritis Community Research and Evaluation Unit
The University Health Network, Toronto, Ontario, Canada
The field of disability research is in need of uniform concepts and a common language to guide scholarly discussion, to advance theoretical work on the disablement process, to facilitate future survey and epidemiological research, and to enhance understanding of disability on the part of professionals as well as the general public. A commonly understood language can also influence the development of public policy in the area of work disability, the focus of the Institute of Medicine’s workshop titled “Survey Measurement of Work Disability.” The current lack of a uniform language and commonly understood definition of the concepts of “disability” and “work disability” is a serious obstacle to all these endeavors.
Conceptual confusion is a particular barrier to the improvement of the Social Security Administration’s (SSA) process for determining eligibility for both Social Security Disability Insurance (SSDI) and Supplemental Security Income (SSI) related to “work disability, ” as was illustrated in the earlier Institute of Medicine workshop, “Measuring Functional Capacity and Work Requirements.” A shared language and conceptual understanding did not emerge from that workshop. If various participants in the disability benefit determination revision process cannot agree on the meaning of the term “work disability,” they can hardly be expected to reach agreement on an approach to improving the work disability determination process.
The Social Security Act defines disability as the “inability to engage in any substantial gainful activity by reason of a medically determinable physical or mental impairment which can be expected to result in death or can be expected to last for a continuous period of not less than 12 months.” As this background
paper will illustrate, this definition in the Social Security Act is at odds with most contemporary thought about the concept of disability and is in itself a barrier to the SSA’s work disability revision process.
The paper presented in this chapter aims to provide the reader with a conceptual foundation to facilitate discussion at the upcoming workshop titled “Survey Measurement of Work Disability.” Our intent is to highlight issues regarding language and concepts directly or indirectly related to the concept of “work disability.” To do so, we focus on several activities:
present a review of some of the contemporary definitions of disability found in the literature;
discuss these definitions in the context of several major disablement frameworks;
discuss the concept of “work disability” in the context of these disablement models and relate it to other health-related phenomena;
critically review the conceptual basis of frequently used survey items that attempt to assess “work disability”; and
highlight some of the pressing research needs in the area of “work disability.”
THE CONCEPT OF DISABILITY
A common understanding of the term “disability” is an essential first step to a scholarly exchange about the concept of “work disability” and is the foundation for a fruitful discussion of improving survey research in the general area of disability and, more specifically, in the area of work disability.
Understanding of the source of contemporary conceptual confusion requires a review of the major disability frameworks found in the literature. The goal of bringing together the several different schools of thought on disability and the disablement process remains elusive. Achieving a commonly accepted conceptual language is one of the primary challenges facing the field of disability research.
Major Schools of Thought
Several schools of thought have defined disability and related concepts. We will focus on the Disablement Model developed by Nagi (1965) and the International Classification of Impairments, Disabilities, and Handicaps (ICIDH-1) (WHO, 1980) and the current proposal for its revision, which is referred to in this chapter as ICIDH-2 (WHO, 1997). We will briefly review both of these conceptual frameworks. Both the Nagi Disablement Model and ICIDH frameworks have in common the view that overall disablement represents a series of related concepts that describe the consequences or impact of a health condition on a person’s body, on a person’s activities, and on the wider participation of that person in
society. In the authors’ view, the major differences in these frameworks are in the terms used to describe disability and related concepts and the placement of the boundaries between concepts more than differences in their fundamental contents. After reviewing the terms within each framework we will compare and contrast the two major models along with their major derivatives and explore how these relate more generally to the concept of “work disability.”
Nagi’s Concept of Disability
According to the conceptual framework of disability developed by sociologist Saad Nagi (1965), “disability is the expression of a physical or a mental limitation in a social context.” In striking contrast to the Social Security Act’s definition of work disability as an inability to work due to a physical or mental impairment, Nagi specifically views the concept of disability as representing the gap between a person’s capabilities and the demands created by the social and physical environments (Nagi, 1965, 1976, 1991). This is a fundamental distinction of critical importance to scholarly discussion and research related to disability phenomena.
According to Nagi’s own words:
[Disability is a] limitation in performing socially defined roles and tasks expected of an individual within a sociocultural and physical environment. These roles and tasks are organized in spheres of life activities such as those of the family or other interpersonal relations; work, employment, and other economic pursuits; and education, recreation, and self-care. Not all impairments or functional limitations precipitate disability, and similar patterns of disability may result from different types of impairments and limitations in function. Furthermore, identical types of impairments and similar functional limitations may result in different patterns of disability. Several other factors contribute to shaping the dimensions and severity of disability. These include (a) the individual’s definition of the situation and reactions, which at times compound the limitations; (b) the definition of the situation by others, and their reactions and expectations—especially those who are significant in the lives of the person with the disabling condition (e.g., family members, friends and associates, employers and co-workers, and organizations and professions that provide services and benefits); and (c) characteristics of the environment and the degree to which it is free from, or encumbered with, physical and sociocultural barriers. (Nagi, 1991, p. 315)
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 the early 1960s. As part of a study of decision making in the SSDI program, Nagi (1964) constructed a framework that differentiated disability (as defined and discussed above) 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.
For Nagi, active pathology involves the interruption of normal cellular processes and the simultaneous homeostatic efforts of the organism to regain a normal state. He notes that active pathology can result from infection, trauma, metabolic imbalance, degenerative disease processes, or other etiology. Examples of active pathology are the cellular disturbances consistent with the onset of disease processes such as osteoarthritis, cardiomyopathy, and cerebrovascular accidents.
For Nagi, impairment refers to a loss or abnormality at the tissue, organ, and body system level. Active pathology usually results in some type of impairment, but not all impairments are associated with active pathology (e.g., congenital loss or residual impairments resulting from trauma). Impairments can occur in the primary locale of the underlying pathology (e.g., muscle weakness around an osteoarthritic knee joint), but they may also occur in secondary locales (e.g. cardiopulmonary deconditioning secondary to inactivity).
To describe the distinct consequences of pathology at the level of the individual, Nagi uses the term functional limitations to represent restrictions in the basic performance of the person. An example of basic functional limitations that might result from a cerebrovascular accident could include limitations in the performance of locomotor tasks, such as the person’s gait and basic mobility, such as transfers, or in nonphysical tasks, such as communication or reasoning. Such functional limitations might or might not be related to specific impairments (secondary to the cerebrovascular accident) and thus are seen as distinct from organ or body system disturbances.
At this point, a “work disability” example will illustrate the distinctions being drawn between the various concepts within Nagi’s Disablement Model. Two patients with Parkinson’s disease may enter the Social Security work disability benefits determination process with very similar clinical profiles. Both may have moderate impairments such as rigidity and bradykinesia. Their patterns of function may also be similar with a characteristically slow, shuffling gait, and slow deliberate movement patterns. Their work role patterns, however, may be radically different. One individual may have restricted his or her outside activities completely, need help dressing in the morning, spend most of the time indoors watching television, be depressed, and be currently unemployed. The other may be fully engaged in his or her social life, receive assistance from a spouse in performing daily activities, be driven to work, and, through workplace modifica-
tion, be able to maintain full-time employment. The two patients present very different work disability profiles yet have very similar underlying pathology, impairment, and functional limitation profiles.
Elaboration of Nagi’s Disablement Model
In their work on the disablement process, Verbrugge and Jette (1994) mainrained the basic concepts of the Nagi Disablement Model and Nagi ’s 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 the following:
Activities of daily living (ADL)—including behaviors such as basic mobility and personal care.
Instrumental activities of daily living (IADL)—including activities such as preparing meals, doing housework, managing finances, using the telephone, and shopping.
Paid and unpaid role activities—including performing one’s occupation, parenting, grandparenting, and being a student.
Social activities—including attending church and other group activities and socializing with friends and relatives.
Leisure activities—including participating in sport and physical recreation, reading, or taking distant trips.
Within their framework, “work disability” is clearly delineated as a specific subdimension under the concept of disability.
In their 1994 work, Verbrugge and Jette attempted to extend Nagi’s Disablement Model to attain full sociomedical scope. They attempted to clearly differentiate the “main pathways” of the disablement process (i.e., Nagi’s original concepts) from factors hypothesized or known to influence the ongoing process of disablement (Figure 2-1).
Viewed from a social epidemiological perspective, Verbrugge and Jette (1994) argued that one might analyze differences in disablement concepts relative to three sets of variables: predisposing risk factors, intraindividual factors, and extraindividual factors. These categories of variables, which are external to the main disablement pathway, can be defined as follows:
Risk factors are predisposing phenomena that are present before the onset of the disabling event and that can affect the presence or severity of the disablement process. Examples include sociodemographic background, lifestyle, and biological factors.
The next class of variables is intraindividual factors (those that operate within a person), such as lifestyle and behavioral changes, psychosocial attributes and coping skills, and activity accommodations made by the individual after the onset of a disabling condition.
Extraindividual factors (those that perform outside or external to the person) pertain to the physical as well as the social context in which the disablement process occurs. Environmental factors relate to the social as well as the physical environmental factors that bear on the disablement process. These can include medical and rehabilitation services, medications and other therapeutic regimens, external supports available in the person’s social network, and the physical environment.
A further elaboration of Nagi’s conceptual view of the term disability is contained in Disability in America (IOM, 1991) and a more recent Institute of Medicine (IOM) disablement model revision highlighted in a report titled Enabling America: Assessing the Role of Rehabilitation Science and Engineering (IOM, 1997).
The 1991 IOM report uses the original main disablement pathways put forth by Nagi with minor modifications of his original definitions. The 1997 IOM report adds two important concepts to the Disablement Model: the concepts of secondary conditions and quality of life. Both of these concepts are discussed later in this chapter.
In 1997, in an effort to emphasize Nagi’s view that disability is not inherent in the individual (as defined by the Social Security Act), but, rather, is a product of the interaction of the individual with the environment, IOM issued EnablingAmerica, in which 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. Figure 2-2 is an illustration of IOM’s 1997 enabling-disabling process.
The IOM report (1997) describes the enabling-disabling process as follows:
Access to the environment, depicted as a square, represents both physical space and social structures (family, community, society). The person’s degree of physical access to and social integration into the generalized environment is shown as the degree of overlap of the symbolic person and the environmental square. A person who does not manifest disability (Figure 2-2a) is fully integrated into society and has full access to both: (1) social opportunities (e.g., employment, education, parenthood, leadership roles) and (2) physical space (e.g., housing, workplaces, transportation). A person with disabling conditions has increased needs (shown as the increased size of the individual) and is dislocated from their prior integration into the environment (Figure 2-2b). The enabling (or rehabilitative) process attempts to rectify this displacement, either by restoring function in the individual (Figure 2-2c) or by expanding access to the environment (Figure 2-2d) (e.g., building ramps). (IOM, 1997, p. 3)
International Classification of Impairments, Disabilities, and Handicaps
Independently from the development of the Nagi model, a similar process was also under way in Europe, which led in the early 1970s to the first draft of what later became the World Health Organization (WHO) ICIDH (WHO, 1980). This model also differentiates a series of related concepts: health conditions, impairments, disabilities, and handicaps (WHO, 1980; Badley, 1993). We will refer to these as the ICIDH-1 concepts. ICIDH-1 is not only a conceptual model; it has also associated with it a hierarchical classification of impairment, disability, and handicap (WHO, 1980). We will not review this classification as such, except to note that, in principle, this system provides a scheme for coding and manipulating data on the consequences of health conditions. This classification and the related model of disablement are being revised and have been named ICIDH-2. At the time of this writing (April 1999), a first, beta draft has been circulated for comment (WHO, 1997), and the beta-2 draft is in the final stages of production. The beta-2 draft revised classification will then undergo 2 years of field testing before the final version is prepared for ratification by the WHO. The changes in the definitions and conceptual model that are being recommended in the process of revision to get ICIDH-2 are discussed below. The U.S. National Center for Health Statistics and the Centers for Disease Control and Prevention have served as the lead U.S. agencies in the international ICIDH revision process.
The first component of the ICIDH-1 model is impairment, which is defined as follows:
In the context of health experience, an impairment is any loss or abnormality of psychological, physiological, or anatomical structure or function. (WHO, 1980, p. 27)
This definition is similar to Nagi’s definition of impairment, but it also includes some of Nagi’s notions of pathology. Just as Nagi’s impairment is focused on organs or organ systems, impairment as defined here is very much concerned with the function and structure of the body and its components. The ICIDH-2 definition is similar:
Impairment is a loss or abnormality of body structure or of a physiological or psychological function. (WHO, 1997, p. 15)
Huge confusion arises because the ICIDH-1 also uses the word disability, but with a slightly different meaning from the Nagi definition of the term. The ICIDH-1 defines disability as follows:
In the context of health experience, a disability is any restriction or lack (resulting from an impairment) of ability to perform an activity in the manner or within the range considered normal for a human being. (WHO, 1980, p. 28)
The focus of this definition is very much on the activities carried out by the person. Further understanding of what is included in this definition can be gained
by inspection of the associated classification (WHO, 1980, 1997). The activities included range from simple functional activities, such as gripping and holding and maintaining and changing body positions, to more complex activities, such as those related to self-care and other ADLs, IADLs, and some of the activity components of other role activities. The latter include, for example, activities that might be carried out in a work environment. Examples from the ICIDH-1 classification include activities such as organizing a daily routine (ICIDH 1980, Code D18.2), use of foot control mechanisms (ICIDH 1980, Code D67), and tolerance of work stress (ICIDH 1980, Code D76). The ICIDH-1 term disability then bridges the Nagi concepts of functional limitation and disability. In revision of the ICIDH, the term disability has been replaced by the positive term activity, which is defined as follows:
Activity is the nature and extent of functioning at the level of the person. Activities may be limited in nature, duration and quality. (WHO, 1997, p. 14)
To prevent further confusion, the rest of this paper will use the term disability solely in the Nagi sense and use the term activity limitation for the ICIDH concept.
In terms of definitions, the construct analogous to the Nagi definition of disability is embodied in the term handicap. This is defined as follows:
In the context of health experience, a handicap is a disadvantage for a given individual, resulting from an impairment or a disability, that limits or prevents the fulfillment of a role that is normal (depending on age, sex, and social and cultural factors) for that individual. (WHO, 1980, p. 29)
As is apparent from the definition, handicap, like Nagi’s disability, also embodies the notion of role. However, by referring to disadvantage it goes further than the actual performance of roles to attach a value judgment, that of disadvantage, to restrictions in role performance. The focus of handicap is the person in the society in which he or she lives and reflects cultural norms and expectations for performance.
The term handicap did not generally find favor, particularly among people who themselves had disabilities, as it carried within it a history of stigmatization (unrelated to its technical definition). In the ICIDH revision process, this questioning of the term handicap spilled over to the whole of the classification and led to the issue of why the emphasis was entirely on the negative. In other words there was a reaction against the whole classification being focused on deficiencies resulting from health conditions. In response to this there has been a switch to neutral terminology, as was illustrated above by the use of the term activity instead of the term disability. In the proposal for revision of the ICIDH, the concept of handicap, as defined above, has been replaced with the term participation, with negative aspects being referred to as restriction in participation:
Participation is the nature and extent of a person’s involvement in life situations in relation to impairments, activities, health conditions and contextual
factors. Participation may be restricted in nature, duration and quality. (WHO, 1997, p. 14)
Like Nagi’s definition of disability, the ICIDH definitions of handicap and participation are essentially relational concepts. This is made very explicit in the ICIDH-2, which states that:
Participation is characterized as the outcome or result of a complex relationship between, on the one hand, a person’s health condition, and in particular, the impairments or disabilities he or she may have, and on the other, features of the context that represent the circumstances in which the person lives and conducts his or her life . . . different environments may have a different impact on the same person with impairment or disability. Participation is therefore based on an ecological/environmental interaction model. (WHO, 1997, p. 17)
The conceptual model that accompanies the ICIDH-2 shows that the context potentially has an effect on the expression of all levels of the model: impairment, activity limitation, and restriction in participation. The context refers both to external environmental factors and to more personal characteristics of an individual. The latter range from relatively uncontroversial characteristics, such as age and gender, to aspects of the person relating to educational background, race, experiences, personality and character style, aptitudes, other health conditions, fitness, lifestyle, habits, coping styles, social background, profession, and past and current experience (WHO, 1997). ICIDH-2 includes a draft classification of environmental factors that covers components of the natural environment (weather or terrain), the human-made environment (tools, furnishings, the built environment), social attitudes, customs, rules, practices and institutions, and other individuals (WHO, 1997). All of the above contextual factors may be relevant, in connection with the impairments or activity limitations of a person, for determining whether that person experiences disability in working or not.
Finally, the ICIDH-2 concept of participation goes beyond the performance of roles and deals with the wider issues of the effect of barriers and facilitators to overall participation in society. In the context of work disability these barriers and facilitators include discrimination, stigma, legislation around workplace design and participation (including the Americans with Disabilities Act), attitudes of coworkers, and extra-work issues such as mobility in the community. This means that an assessment of restriction of participation does not necessarily need to be on a personal basis and might, in some situations, be predicted by direct assessment of barriers. For example, workplaces that are not accessible to wheelchair users would systematically restrict participation, irrespective of the nature and demands of the actual work tasks.
THE CONCEPT OF SOCIAL ROLES
To understand fully how Nagi’s definition of disability and the ICIDH definition of handicap can be applied to the area of work disability, one must under-
stand the concept of social role and tasks from a sociological perspective. Social roles, such as being a parent, a construction worker, or a university professor, are basically organized according to how individuals participate in a social system.
According to Parsons (1958), “role is the organized system of participation of an individual in a social system” (p. 316). Tasks are specific activities through which the individual carries out his or her social roles. Social roles are made up of many different tasks, which may be modifiable and interchangeable. For Nagi, the concept of disability is firmly rooted in the context of health. Thus, for Nagi (1991), health-related limitations in the performance of specific social roles are what constitute specific areas of disability, work being one important area of disability. Roles such as work can be disrupted by a variety of factors other than those that are health related. A change in the economic climate or technological changes, for example, may lead to unemployment totally unrelated to health conditions. These would not represent work disability in the way that Nagi defines this term. As Parsons clarifies:
Roles, looked at that way, constitute the primary focus of the articulation and hence interpretation between personalities and social systems. Tasks on the other hand, are both more differentiated and more highly specified than roles, one role capable of being analyzed into a plurality of different tasks. . . . A task, then, may be regarded as that subsystem of role which is defined by a definite set of physical operations which perform some function or functions in relation to a role. (Parsons, 1958, p. 316)
Are there limits to this concept of disability from the perspective of role performance? Nagi argues that components of roles—expectations or specific tasks that are learned, organized, and purposeful patterns of behavior—are part of the disability concept. They are more than isolated functions or muscle responses (Sarbin and Allen, 1968; Nagi, 1991). Some tasks are role specific, whereas others are common to the enactment of several roles. For Nagi, to the extent that these tasks are learned, organized, and purposeful patterns of behavior, they are part of the disability concept. It is for this reason that Nagi views the concept of disability as ranging from very basic ADLs to the exquisitely complex social roles such 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 2-3). 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 accessible modes of transportation to the workplace, environmental barriers in the workplace, or the willingness of the employer to modify the individual workstation to accommodate a health condition. Viewed from the perspective of role performance, degree of work disability could be reduced by improving the individual’s capacity to accomplish functional activities—a very traditional view of rehabilitation—or by manipulating the physical or social environment in which work occurs. A discussion similar to that given above could be formulated by using the language of the ICIDH.
The fundamental conceptual issue of concern is that a health-related restriction in work participation may not be solely or even primarily related to the health condition itself or its severity. In other words, although the presence of a health condition is a prerequisite, “work disability” may be caused by factors external to the health condition’s impact on the structure and functioning of a person’s body or the person’s accomplishment of a range of activities.
DIRECTIONALITY AND THE DYNAMIC NATURE OF DISABILITY
The earliest disablement models represented by the ICIDH-1 formulation (WHO, 1980) and Nagi’s disablement model (Nagi, 1965) presented the disablement process as more or less a simple linear progression of response to illness or consequence of disease. One consequence of this traditional view is that disabling conditions have been viewed as static entities (Marge, 1988). This traditional, early view of disablement failed to recognize that disablement is more often a dynamic process that can fluctuate in breadth and severity across the life course. It is anything but static or unidirectional.
More recent disablement formulations or elaborations of earlier models have explicitly acknowledged that the disablement process is far more complex (IOM, 1991, 1997; Verbrugge and Jette, 1994; WHO, 1997; Fougeyrollas, 1998). These more recent authors all note that a given disablement process may lead to further downward-spiraling consequences. These feedback consequences, which may involve pathology, impairments, and further limitations in function or disability, have been explicitly incorporated into the graphic illustrations of more recent disablement formulations. The 1991 IOM report uses the term secondary conditions to describe any type of secondary consequence of a primary disabling condition. Commonly reported secondary conditions include pressure sores, contractures, depression, and urinary tract infections (Marge, 1988); but it should be understood that they can be either a pathology, an impairment, a functional limitation, or an additional disability.
Longitudinal analytic techniques now exist to incorporate secondary conditions into research models and are beginning to be used in disablement epidemiological investigations (Lawrence and Jette, 1996).
HOW DISABLEMENT CONCEPTS DIFFER FROM QUALITY OF LIFE AND SIMILAR CONCEPTS
To compare disablement concepts with the phenomenon of quality of life, one must first consider how quality of life has been defined in the literature. Birren and Dieckermann have provided a useful starting point:
The concept of quality of life is complex, and it embraces many characteristics of the social and physical environments as well as the health and internal states of individuals. There are two approaches to the measurement of quality of life: One is based upon the subjective or internal self perceptions of the quality of life; the other approach is objective and based upon external judgments of the quality of life. (Birren and Dieckermann, 1991, p. 350)
If we apply Birren and Dieckermann’s perspective to work roles and work disability, objective dimensions of quality of life might include whether a person has had to change jobs because of a health problem, whereas the subjective dimension might include the individual’s satisfaction with his or her job. Consis-
tent with this objective and subjective view of quality of life, Lawton (1983) has suggested that measures of quality of life should include a multidimensional evaluation of both intrapersonal and social-normative criteria including:
perceived quality of life,
behavioral competence in multiple areas (i.e., health, functional health, cognition, time use, and social behavior), and
the objective environment itself.
Indicators of quality of life are extremely broad and have included standard of living, economic status, life satisfaction, quality of housing and the neighborhood in which one lives, self-esteem, and job satisfaction. Such a broad concept subsumes many dimensions of personal well-being not directly related to health.
In response to concerns about the breadth of overall quality of life, some health researchers have adopted a narrower concept called “ health-related quality of life.” Health-related quality of life has been defined in line with WHO ’s definition of health as a state of complete physical, mental, and social well-being, not merely the absence of disease or infirmity (WHO, 1947). Major dimensions in the health-related quality-of-life measures include signs and symptoms of disease, performance of basic physical activities of daily life, performance of social roles, emotional state, intellectual functioning, general satisfaction, and perceived well-being.
Some models of disablement such as the IOM formulation (IOM, 1991, 1997) and Patrick’s (1997) conceptual work clearly define quality of life as distinct from the disabling process. As IOM describes it:
Quality of life affects and is affected by the outcomes of each stage of the disabling process. Within the disabling process, each stage interacts with an individual’s quality of life; it is not an endpoint of the model but rather an integral part. (IOM, 1991, p. 8)
This view of quality of life strikes the authors as inconsistent with the definitions of quality of life described previously and may create problems in designing appropriate survey measures. The concepts of quality of life and health-related quality of life, in particular, appear to overlap and include within their boundaries many (yet certainly not all) of the disablement concepts reviewed in this chapter. Like the disablement concept, quality of life includes dimensions at the personal activity and social role levels. Like the disablement concepts, quality of life does direct some attention to the concepts of disease, through an assessment of signs and symptoms. Most quality-of-life measures focus little attention on organ and body system functioning and focus more on the consequences of impairments at the personal activity or social role level. At the level of social roles, quality-of-life dimensions are broader than the disablement concepts that incorporate overall life satisfaction, energy, vitality, and emotional well-being (Levine and Croog, 1984).
Thus, the authors have difficulty viewing the concept of quality of life as entirely distinct from several dimensions in the disablement concepts. For some elements of quality of life, disablement is clearly a precursor, but other elements fall outside the disablement formulation. There appears to be considerable overlap between elements of the two formulations, and a conceptualization that acknowledges this overlap may be a more useful formulation (Figure 2-4).
CONCEPTUAL ISSUES RELATED TO THE MEASUREMENT OF WORK DISABILITY
The underlying structure of models of disablement, as currently conceived, maps a pathway between the health condition and the ensuing “work disability” or other restrictions to social participation. Close inspection of the definitions given above suggests that a number of steps can be identified in the pathway between the health condition and the social consequences described as work disability. At a micro level there are the pathological changes in the body and impairment in the structure and functioning of organs and body systems. There may be an impact on the activity of the person, ranging from simple movements, to basic activities of daily living, to instrumental activities of daily living, and so on. These can then contribute to the performance of more complex social roles, and ultimately, the person’s participation in all aspects of society can be adversely affected. Work is one such social role.
Both the Nagi and the ICIDH models cover the spectrum of the consequences of health conditions. As indicated earlier, as well as terminology, a major difference is where these models place the boundaries between the different concepts (see Figure 2-3). In the Nagi model the performance of all activities, except for basic actions or functions of the body, are subsumed into the overall category of disability (Nagi, 1976). In the ICIDH model the concept of activity includes these basic actions as well as ADLs, IADLs, and some other role activities (with the emphasis very much on activity) (WHO, 1980, 1997; Badley, 1993). Participation is reserved to highlight the way in which the performance of activities may be constrained by more than the immediate context of the activity. The juxtaposition of the two models in this way illuminates some nuances in the ways in which the impact of health conditions can been conceptualized as having an impact on the overall functioning of the individual. As indicated earlier, work disability is a function of whether the person can perform specific work-related tasks and of external factors. From the point of view of the measurement of work disability, it may be useful to distinguish between the degree of difficulty that a person may have in carrying out an activity and these other factors (such as barriers in the environment, attitudes of employers or coworkers, and other restrictions) that might prevent the performance of those activities in daily life. In this way, the levels of impact described within the conceptual models are of importance as they allow us to locate where many of the current types of assessment of work disability might fit in.
In the authors’ view, in general, no explicit conceptual framework appears to be used in the ascertainment of work disability. A number of implicit conceptual approaches appear to have been used to assess and identify people with possible work disabilities. Each approach can be compared to the different levels of a model of disablement as discussed in the previous sections. We will review these in turn. However, before we do this we need to deal with some more general issues.
Discrete or Continuous Phenomena
Disability is commonly presented as an all-or-nothing phenomenon; either a person has a disability or a person does not. In reality, disability (in particular, roles or activities) is usually encountered in terms of degree of difficulty, limitation, or dependence, ranging from slight to severe. The question then becomes: where on the disability spectrum is that threshold that determines if a person is disabled? This needs to take into account any assistive devices or accommodations that the person may have. In the current context, work participation is often determined as being an endpoint, in that people either have a work disability or they do not. In reality, the situation is likely to be more complex. For example, many people with functional and activity limitations may continue to work, but their labor force participation may be compromised in some way by the condition. To the extent that it is, these people might be said to have some degree of work disability. In measuring work
disability, a clear definition of the threshold used needs to be made. Alternatively, a continuous measurement needs to be undertaken.
Duration or Chronicity
There is a pervasive assumption that work disability is a long-term state. Stereotypes about disability are dominated by the archetype of a person who uses a wheelchair. Embedded in this is the notion of some disabling event, a period of adjustment and rehabilitation, and then the resumption of as full a life as possible with the assistance of any necessary assistive devices or accommodations. With many impairments, the reality of disability is somewhat different. The majority of individuals in the working-age population with long-term activity restrictions report that this restriction is due to musculoskeletal, circulatory, or respiratory disorders (LaPlante, 1996). These conditions may also be associated with varying degrees of “illness,” so that it is not just an issue of physical performance. There are also considerations of pain, fatigue, and other symptoms. Many of these conditions are episodic in nature and may have trajectories of either deterioration or recovery (the latter being less common). This means that, apart from any environmental barriers or facilitators, the day-to-day or month-to-month experience of disability may be variable. This may need to be taken into account in any measurement scheme.
Examples of Conceptual Approaches to Measuring Work Disability
All disablement concepts appear to have been addressed, at least to some extent, as part of efforts to assess work disability.
Health Condition or Pathology
Under some circumstances knowledge of the health condition or pathology contributes to an assessment of work disability. Medical listings of diagnosis and medical severity have been used by some agencies to identify individuals who would be unlikely to benefit from vocational rehabilitation (Reno, 1999). Such listings have also been applied in the context of Social Security disability determinations. Concern has been expressed because the use of such listings might, on the one hand, deny benefits to individuals who need them and might, on the other, award benefits to those who could still work. Such concerns are a reflection of the many steps in the disablement model between the health condition and work disability.
Assessments of work disability, or at least of entitlement to compensation for work injury, are often made at the level of impairment. The classic assessment is
perhaps what has been pejoratively referred to as the “meat chart” assessment of the consequences of traumatic injury. An example of this would be the American Medical Association Guides to the Evaluation of Permanent Impairment (American Medical Association, 1993), which is a standardized system for translating the extent of an injury of a body part into a percentage of disability of the whole person. This type of system has been used for the assessment of compensation payments, including for workers ’ compensation.
A number of assessments focus on the functioning of the body, for example, assessments of strength, muscular endurance, body coordination and flexibility, and cognitive and sensory functions (Fleishman, 1972, 1999). The problem with this impairment-focused approach is that even though these assessments may be made in the context of relating functional requirements with the requirements of certain jobs, one needs empirical evidence to support the contention that the degree of impairment is going to have a direct relationship to work disability. Without such evidence, the validity of such an approach is highly suspect.
Much of the discussion of assessment of work effectively has been at the level of functional disability. An example would be the assessment of abilities proposed for the Occupational Information Network (O*NET) system (see, for example, IOM, 1999, p. 24). Here abilities such as oral comprehension, memorization, finger dexterity, and depth perception (IOM, 1999, p. 35) will be assessed and compared with the average requirements of particular jobs. Although the intent was that this should be done for all jobs, it has been suggested that this approach could, in principle, provide the basis of an assessment of work disability (IOM, 1999, p. 86). Measures of work-related functional capacity (Lechner et al., 1997) have also been devised to test or ask about activities such as lifting, standing, walking, sitting, and carrying. Although closer in concept to work disability than assessments of pathology and impairment, assessments of capacity to perform work functions are one level removed from the concept of work disability. They look at the specific abilities of the individual for work in standardized ways not directly related to actual work settings. More importantly, they take no account of any environmental barriers or facilitators that might moderate the way in which a person ’s functional limitations are expressed as disabilities.
Activity Limitation (at Work)
A direct way of answering at least part of the question about work disability is to carry out a workplace assessment. This gives information about whether the person can actually carry out the requirements for the major components of the job. This is the kind of assessment that is frequently carried out in the context of vocational rehabilitation. However, factors other than the actual performance of
the work tasks likely contribute to work disability as indicated earlier. This is further discussed below.
Having separated out the activity limitation in work tasks, one can look at work disability from the perspective of carrying out a work role. Direct assessment of work disability involves several elements related to the role of work. These include:
activities within the workplace;
a range of other aspects including necessary mobility in getting to work;
interaction with colleagues, superiors, and subordinates; and
the amount and type of work that can be carried out.
Work disability is most frequently assessed by direct inquiry of the individual. The measurement problems with this kind of approach are reviewed in Chapter 3. In population surveys the two main types of approaches to measurement of work disability are either (1) direct questioning about any limitations in work attributable to a health condition or (2) the independent ascertainment of disability and work status, with some inference of a connection between disability and work status. We will review each of these in turn.
DIRECT ASSESSMENT OF WORK DISABILITY
The most direct approach to ascertainment of work disability is to inquire about working status together with questions as to whether nonparticipation is health related. There are various permutations on these types of questions. Some typical formulations are shown in Figure 2-5.
As Figure 2-5 illustrates, typical survey questions about work disability are asked with a general reference to work, and it is left to the respondent to determine the specific relevant elements to be considered within the work role. If the respondent is currently working or has recently worked, this is presumably taken to mean the most recent working experience. If the person is not working, then this is more problematic. The answer to the question will depend on what type of employment, if any, the individual has in mind when answering the question. If the purpose of the question is to determine incapacity for work, then the nature of the job and any accommodations that have been or might be made is crucial. Few survey research approaches break down work role into its major component parts to determine the perceived degree of disability within each.
Typical survey research questions also leave it to the respondent to attribute not working to an underlying health condition. It may be that the individual answers that he or she cannot work, yet the person may not be given the opportunity to specify the circumstances under which this might be possible. A survey of
working-age people with disabilities in the United States showed that over two-thirds wanted to work (Stoddard et al., 1998, p. 24). In the 1991 Canadian Health and Activity Limitation Survey, 64 percent of respondents with disabilities reported that they were not in the labor force, and over two-thirds of these said that they were completely prevented from working (Statistics Canada, 1993). However, all respondents were given the opportunity to answer questions about needed accommodations in the workplace. Despite reporting that they were prevented from working, 69 percent of these individuals reported needing a variety of workplace accommodations (e.g., job redesign or modified hours) and 76 percent reported needing adaptations (e.g., handrails, elevators, or modified workstations). Whether or not the provision of such accommodations or adaptations would facilitate workplace reintegration is unknown. However, the findings illustrate how changing the framing of a question sheds a different light on what it means to be unable to work. Individuals who were not in the labor force were also asked about barriers to employment. The most frequently mentioned barriers were losing some or all of their current income, feelings that their training was not adequate, no available jobs, and loss of additional supports (e.g., health benefits). Other less frequently mentioned reasons were family responsibilities, having been the victim of discrimination, and not having accessible transportation (Statistics Canada, 1993). In other words, most of the reasons were related not to the nature of the work, but to some of the other circumstances surrounding the issue of work disability.
Furthermore, some individuals will have a choice as to how they describe their working status. For example, a person with a disability who also has small children could variously describe him- or herself as a homemaker or not being in the labor force because of the disability. Or people leaving the workforce in their 50s may describe themselves as having taken an early retirement. Without extra information it may be difficult to tell whether this is indeed the situation or whether the alternative description was seen as a less stigmatizing alternative to describing themselves as having a work disability.
In a survey research situation, if a person is working, the typical approach is to assume that no work disability is present. Nevertheless, the person may be limited in the amount or kind of work done or both. The person may be spending less time working, working at a less skilled job, or earning less money. This information can be obtained from survey questions (see Figure 2-5), but often with relatively little qualifications as to what this means. What is less often addressed is that for many people with disabilities working may mean forgoing opportunities to participate in other areas of life. Just going to work may, for example, exhaust all reserves of energy or require time-consuming preparations. There is a fine line between what might be considered a satisfactory accommodation and an unsatisfactory compromise or necessity, and different people will value this trade-off differently.
The problem with all the approaches to work disability, as indicated by our discussion of conceptual frameworks, is that there is unlikely to be a one-to-one relationship between the presence of health conditions, impairments, functional limitations, or activity restrictions and disability in employment. There is a pervasive assumption that work disability relates to the person’s degree of functional limitation and activity restriction. This is reflected in the concern about assessment, where the focus is very much on the individual’s performance. Lip service is paid to the environment, particularly in the context of work disability and vocational rehabilitation. As we have tried to show, a full understanding of work disability needs to take into account the individual’s circumstances and the social and physical environments of the workplace.
The research challenge is to apply the insights provided by the models of disablement to come to a common understanding of work disability and to understand the relationships and the dynamics of the pathway between health conditions and work disability. Researchers need to find ways to incorporate an understanding of the external factors that influence the development of work disability into its measurements.