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National Research Council (US) Committee on National Statistics; National Research Council (US) Committee on Population. Improving the Measurement of Late-Life Disability in Population Surveys: Beyond ADLs and IADLs, Summary of a Workshop. Washington (DC): National Academies Press (US); 2009.

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Improving the Measurement of Late-Life Disability in Population Surveys: Beyond ADLs and IADLs, Summary of a Workshop.

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APopulation Survey Measures of Functioning: Strengths and Weaknesses*

Barbara M. Altman


Thomas (2002) has pointed out that “disability” is a common term whose meaning is seen as beguilingly obvious to the layperson—not being able to do something. However, the legislative use of the term in policy and the scientific use of the term in medical, rehabilitation, or welfare settings to define the relevant population is fraught with shades of meaning that vary according to the purposes of those activities. Meaning is also influenced by the way people conceptualize and measure within those purposes. These multiple, as well as different, approaches to the understanding of the terms of discussion obscure theoretical definitions and confuse communication when one tries to examine the big picture.

Since scientific disciplines tend to work within the bounds of their own literatures, terminology, and models, these variations in definition, measurement, and meaning persist. The history of the involvement of many disciplines in the development of policy and programs to address disability issues—medicine, education, social work, psychology, sociology, vocational counseling, occupational and physical therapy, and others—sets the stage for attempts at conceptual distinctions to delineate measures of the disability process (Nagi, 1991). Importantly, even when definitional components are generalized and accepted across fields (such as with the International Classification of Functioning, Disability and Health [ICF]), measurement of those components in terms of disciplinary practice reintroduces different shades of meaning and alters the conceptual definition in subtle but specific ways.

The purpose of this paper is threefold. First, I explore the disability conceptualization/measurement continuum in the area of population surveys, to locate it within the general theory of disability and to compare it across specialty areas of application. Second, I define and locate the source and types of measurement for the variety of theoretical concepts associated with the disability process. Finally, I reintroduce the important contribution of the social and environmental context not only to the conceptualization of disability, but also to its measurement.


Among other things, the lay “beguiling” meaning of disability generally locates the source of the problem within individuals, based solely on their physical or mental impairment or imperfection. This personal attribution comes in part from the medical orientation to chronic conditions and the physical or mental impairment consequences of those conditions which focus both diagnosis and treatment on individuals. Although diagnosis and treatment are appropriately directed toward the chronic condition or impairment a person exhibits (consideration of the individual as the host of a problem), locating the larger phenomenon of “disability” within the individual in the same way is inappropriate and misrepresents the situation. There are actually at least three major component areas that contribute to creating a disabling outcome, and none of them is located within the person.

The medical model, which has influenced so many of the nation’s disability-related programs, is not so much a separate theoretical model but the primary context in which the available theoretical models have been interpreted through research and applied in programmatic activity. The emphasis is placed on the physical or mental impairment within the person, assuming it is the sole factor that somehow constrains activity and access. The medical model begins in a medical setting, with the emphasis on diagnosis, treatment, and rehabilitation of people as they move from active pathology to impairment. Given the medical orientation, the medical model also is a form of data collection, such that the source of data is a physical examination or observed performance.

Following the initial stages of the disability process that grow out of the relationship with medical organizations, disability-related programs, many of which were structured in an earlier time, continue the focus on the individual, ignoring the culpability of society and the environment. So, for example, the organization of the Social Security program was focused on replacing the person’s monetary support base and not on retraining them for a different kind of job or providing a legislative agenda to prevent discrimination in the job market. With the emphasis on replacing income, stringent eligibility criteria, which required medical documentation, were necessary because of the potential long-term costs of the program. Vocational rehabilitation continued this focus on the person but broadened it to include training, medical care, and therapy—all directed at the person—rather than seeking to remove structural and social barriers by rehabilitating the workplace as well.

As early as the late 1980s, individuals and groups were pointing to problems with emphasizing the individual in the disability equation (Caplan, 1988). It was a very hard sell; however, Disability in America (Institute of Medicine, 1991) did give space to the idea. Nonetheless, the emphasis in that groundbreaking work was still the person, not only the conditions causing disability, but also the problem of secondary conditions that could make a disability worse. Because the mandate of that volume was to explore the prevention of potentially disabling conditions from developing into disability at every stage of the disability process, the emphasis was heavily weighted toward what could be done for the person in the medical context, from the prevention of secondary conditions to the use of rehabilitative and vocational services.

The contribution of Verbrugge and Jette (1994) in their elaboration of the disability models in use at the time (Nagi, 1965; World Health Organization, 1980) was the beginning of bringing the understanding of the disability process beyond the medical context. Moving the theoretical models beyond the medical context laid the groundwork for also moving the data collection about the process into a social survey context. The expanded 1996 Medical Expenditure Panel Survey and the 1994–1995 National Health Interview Survey on Disability (NHIS-D) solidified that position. They also added nationally representative data on disability, which included broader sets of questions and the whole population, to what had previously been specialty surveys on particular populations, such as Social Security recipients, children, or the aging population.


Nagi Model

Several models allow us to examine the elements of disability and explore where they are located and how they relate to one another. The original model that gained widespread acceptance was authored by Nagi and included the conceptual elements of pathology, impairment, functional limitation, and disability (Nagi, 1965). Although Nagi never presented his theoretical model in a symbolic format, others have, implying a unidimensional progression from pathology to an outcome called “disability.” However, a close and careful reading of the original Nagi theoretical exposition (Nagi, 1965) and later works (Nagi, 1969, 1991) can be interpreted somewhat differently, symbolically as well as conceptually. Moreover, key constructs presented by Nagi—role interactions and behaviors—are omitted altogether from most secondary interpretations. I have elaborated the symbolic representation accounting for the role interaction situation Nagi originally postulated and emphasizing the individual’s behaviors that follow. It is this pattern of behavior that Nagi defined as disability (Altman, 2001b). These conceptual subtleties, which are frequently glossed over, are discussed here.

There are several important points to take from the Nagi model that are relevant to the definition and measurement of disability in survey situations (see Figure A-1). First, disability is not the equivalent of an individual’s conditions or impairments, be they pathologies, residual losses, or abnormalities caused by injury, disease, or congenital accident. Conditions and or impairments are attributes of the individual that eventually affect the nature and degree of disability through their effects on the person’s overall functioning. Rather, disability refers to social outcomes. It is related to performing socially defined roles,1 from self-care to employment, and is shaped by the expectations, reactions, and definitions of people around the “disabled” individual, as well as by the impact of the physical environment. It reveals itself most completely in the behaviors exhibited by an individual in social situations (Nagi, 1965).

FIGURE A-1. Two versions of Nagi model.


Two versions of Nagi model. SOURCE: Altman (2001b).

Although Nagi changed this definition of disability somewhat in later work (Nagi, 1991) to reflect a more social functioning orientation, the broader orientation of his earlier work is used in this paper as well as the later one because of its importance in measurement. Although the differences between “functioning” in a role and “behavior” in a role may seem quite subtle, they are important differences in understanding the full effects of the environmental contribution to disability. Questions based on a functioning perspective still locate the problem primarily in the person’s ability to do the activity within the given context, such as being limited in the kind or amount of work or unable to work. Questions about behavior can more accurately reflect the adjustments that are made both by the person and in the context and also reflect the person’s choice in the situation. Functioning reflects assessment of ability or capacity in the general situation, whereas behavior is the manifestation of the actual interaction that creates disability. While functioning in basic actions, such as walking or seeing, is an important component of the equation at the person level, functioning in the area of a more complex activity, such as working, focuses on the outcome of the person–environment interaction. This latter functioning tells us what the person can do in such a situation or the difficulty they have doing it, but it tells us nothing about how their behavior has been modified to accommodate the barriers or how the barriers have been modified to accommodate the functional limitation.

The strength of the Nagi model lies in its insights about the whole process, which still have relevance after more than 40 years. Two areas are particularly important. First, the recognition of the difference between impairment, the damaged organ, cell, or body part, and functioning, actions of the whole person, which focuses the measurement on the person’s capacity rather than the type of condition extant within the person. This differentiation identifies functioning as the fulcrum in the disability process.2 The other area of strength is acknowledgment of the important role that social interaction with friends, family, and the community contributes to defining the situation. Although the physical environment is not mentioned in the original discussion of the model, it is certainly addressed in the study of disability and rehabilitation, the source of the “Nagi questions,” which were written a few years later (Nagi, 1969). The weakness seems to be the lack of further conceptual elaboration of the behavioral component sufficient to provide clues to its measurement.

Institute of Medicine Models

Two other commonly referenced models are the Institute of Medicine (IOM) model from Enabling America (Institute of Medicine, 1997) and its predecessor from Disability in America (Institute of Medicine, 1991). Both are products of the IOM committee process. Both are based on the Nagi model and the later version is very much influenced by adaptations of the Nagi model by Verbrugge and Jette (1994).

The 1997 IOM model depicted in Figures A-2 and A-3 follows the Nagi model concepts closely in the areas of pathology, impairment, and functional limitation and collapses some of the Verbrugge and Jette elements of intra- and extra-individual factors into the quality-of-life components (Verbrugge and Jette, 1994). Disability is addressed separately (see Figure A-3) from the overall model to emphasize the interactive nature of its creation and, one assumes, to focus attention on the complexity of a process that is easily ignored. What is indicated clearly in this part of the model is that disability is not inherent in the person, but rather a result of the interaction of the individual and the environment. In other sections of the IOM text, reference is made to adjustments to the physical environment or rehabilitation of the individual, both of which can contribute to modifying the level of disability a person experiences.

FIGURE A-2. Second Institute of Medicine model.


Second Institute of Medicine model. SOURCE: Institute of Medicine (1997), adapted from the first model (Institute of Medicine, 1991).

FIGURE A-3. Complementary component of Institute of Medicine model: Conceptual overview of the person–environment interaction and how that interaction creates the disability.


Complementary component of Institute of Medicine model: Conceptual overview of the person–environment interaction and how that interaction creates the disability. SOURCE: Institute of Medicine (1997).

The strengths of the IOM model include its reinforcement of the Nagi separation of impairment and functioning and the provision of a much clearer presentation of the person–environment interaction that leads to disability. The latter is particularly meaningful for measurement purposes because it broadens the measurement potential beyond individual functioning and an independence–dependence dichotomy—represented by activities of daily living (ADLs) and instrumental activities of daily living (IADLs)—to the person–environment context. The IOM discussion acknowledges the multidisciplinary character of the study of disability by very efficiently pointing to cultural, psychological, economic, and political questions that need to be addressed (Institute of Medicine, 1997, p. 168). However, although the model moved forward an understanding of the process, particularly the contribution of the external environment, it lacked insights into actual mechanisms associated with this environment–person interaction. This leaves a gap in the measurement process for environmental elements without a clear direction for the conceptual operationalization process. As with the ICF model that follows, the importance of environment is clear, but where to start the measurement process is vague.

International Classification of Functioning, Disability and Health Model

ICF (World Health Organization, 2001a) is an extensive revision of the International Classification of Impairments, Disabilities, and Handicaps (World Health Organization, 1980), both products of the World Health Organization. This final model of the disability process currently in use (shown in Figure A-4), like the IOM model, does not include the state of “disability” within the outlines of the conceptual relationships. It also does not include the concept of functioning limitation so prominent in the other two models.

FIGURE A-4. ICF model.


ICF model. SOURCE: World Health Organization (2001a).

Disability in this model is an umbrella term for the negative aspects of the interaction between an individual and that individual’s contextual factors, while functioning is the umbrella term used to denote the positive aspects of the interaction between an individual in his or her context. The conceptual elements in this model reflect, for the most part, the elements of body structure and function (identifying the impairment as well as the body system or body part where it is located), activity (which represents a person’s execution of a task or action—the individual perspective of functioning), and participation (which represents a person’s involvement in a life situation, functioning at a complex level of activity). However, there are continuing problems differentiating the activity and participation components for use when applying the conceptual model in practice, as in the case of measurement (Chapireau, 2005; Whiteneck, 2006; Institute of Medicine, 2007). Environmental factors are noted, along with personal factors as modifiers of the whole set of concepts similarly to the use of biology, environment, lifestyle, and behaviors as risk factors in the IOM model.

The ICF model, which has received international support, also provides a taxonomy for classifying function, disability, and health with standard concepts and terminology. It provides an extensive set of domains that represent the three primary areas of the model: body function and structure, activity and participation, and environmental factors. The domains are accompanied by a coding scheme that allows for classification of a person’s characteristics at four different levels of specificity. In addition, there is also a coding scheme to denote qualifiers to represent the level of severity of the problem in the case of an impairment or the degree of barrier located in the environment. There are also optional qualifiers and a set of rules for their application. These domains and codes are posited as a measuring function, but it is misleading: although they may be useful in clinically oriented measurement associated with the body function and body structure sections, they are open to wide differences in operationalization in the activity and participation sections.

ICF moves the field forward through the standardization of some terminology and the specification of domains or areas that can be considered points of operationalization for measurement purposes. However, the use of disability and functioning as umbrella terms creates as much confusion as clarity when they are used to represent everything. The emphasis on the body function and structure compliments the health condition classification of ICD-10 and makes the ICF classification a promising tool for clinical settings. However, from a social survey perspective, this emphasis on body structure and function, combined with the lack of differentiation between activity and participation, confuses the development of measurement to represent the process. The environmental context is viewed so broadly as to provide little guidance for measurement purposes.

All three models are similar in that they identify some form of impairment, individual functioning, and societal participation in an environmental context as the key components involved in disability (some more clearly and others more broadly). The ICF model has difficulty providing a clear demarcation between activity and participation, but it provides a classification schema with an extensive set of domains to be considered. Although the Nagi and IOM concepts of functioning are directed more specifically at the whole person’s basic actions than is the ICF, the Nagi concept of “disability” and the IOM concept of “disablement” are less specific and much more open to a wide range of possible interpretations from a measurement point of view. Environment in all three models is expressed in very broad brushstrokes, with emphasis in the Nagi model on the interaction with significant others or role sets;3 in the IOM model on physical modifications and vague definitions of social factors; and in the ICF model to all aspects of the extrinsic world that can contribute to the context in various settings. The last, though accurate, makes it nearly impossible to select a meaningful measure in a simple, concise way necessary in survey work.


Locating the Point of Measurement

The first concept considered here is the pathology or condition that is the causative health problem for creating whatever impairment may result. This element is located within the person’s physical, mental, or emotional organs or organ systems; see Figure A-5. The pathology or condition is a health problem, an injury, or a congenital defect. It is the focus of diagnosis and treatment in the medical context. It takes place or is found in the person in one or more sites in or on the body. It is not a disability, although it can be a precursor to disability by causing an impairment that can inhibit functioning. So in the Nagi symbolic model (as adapted; see Altman, 2001b) and the IOM model, both the pathology and the impairment are located at the person level. In the ICF model, health or disease is presented as an intervening variable, and body function and structure represent the impairment and its location as the link with the International Classification of Disease. All three models identify the pathology, condition, and impairment in the person; thus measurement should be operationalized at the person level.

FIGURE A-5. Impairment, located within a person.


Impairment, located within a person.

The second concept for consideration is limitation in functioning; see Figure A-6. In Nagi’s interpretation these are “limitations which impairments set on the individual’s ability to perform the tasks and obligations of the usual roles and normal daily activities” (Nagi, 1965, p. 102). The emphasis is on the individual performing the basic actions necessary to accomplish everyday tasks, roles, and obligations. This refers to the ability of a person to perform the building blocks of action, such as walking, communicating, making decisions, and so forth. This type of functioning difficulty is not condition or impairment specific, but it may be common to several different types of conditions or impairments. For example, people with severe heart disease can have problems walking any distance, which is similar to people with orthopedic problems. In this instance, the conceptual focus is on the whole person and the functioning or accomplishment of the basic action, which requires coordination of physical, mental, and emotional capacities, and the choice or will to do it is concomitant with the person rather than one or more body parts. Mechanical aids to help with functioning are useful tools, but they reflect an environmental accommodation. In terms of measurement, functioning should be assessed without the use of aids in order to reflect the person’s fundamental capacity.

FIGURE A-6. Functioning, located at the level of a person.


Functioning, located at the level of a person.

The ICF model collapses actions and tasks into one conceptual component, activity. It does not separate the physical, cognitive, and emotional functioning from the tasks that require such individual functioning to be accomplished. The Nagi idea of individual functioning can be considered to be captured in the activity conceptualization of the ICF model, but the activity concept includes much more as well. In the ICF chapter on mobility, moving around is not only conceptualized as the basic action of walking but also as the organized activity of using transportation to move around, which requires a combination of different types of individual functioning ability other than just the basic ability to walk. Although this is an adequate approach to conceptualizing a hierarchy for a classification scheme, it confuses the hierarchy of a measurement process. Walking can be understood as a basic building block of action at the person level, but accomplishing a task, such as using transportation, in addition to combining the capacity to walk with other actions (such as cognitive functioning) to locate transportation, also requires making a choice as to what kind of transportation, involves seeing or hearing in order to use a schedule and so forth. Thus, using a transportation system not only represents using multiple areas of functioning, but also is influenced by a cultural component that creates the types and availability of transportation as well as the expectations for how those forms of transportation are to be used. It represents a much more complex activity; and thus involves increased issues associated with measuring (see Figure A-6).

The complement to this functioning capacity, which Nagi (1965) addresses but is omitted from newer models of disability, is the cultural component, the agreed-on nature, requirements, and expectations of the roles and activities a person is attempting. So, for example, bathing in a developing country may require very different functioning abilities than bathing in the United States, such as having to walk half a mile to the nearest body of water. Roles of spouses and parents may also differ; some may be flexible and allow a variety of ways to fulfill the role expectations; others may be more fixed or rigid, requiring specific functional capacity that a person can no longer accomplish. Functioning is the linchpin for the individual’s behavior, but the culture is what creates the expectations that need to be addressed by that behavior.

A further word about the idea of functioning: Functioning is a versatile concept and can be applied at many levels of activity, from the simplest to the most complex. Therefore, “functioning” is one of the more ambiguous terms used in the discussion of disability, one that contributes to the confusion that is created by the use of language to represent these concepts and their translation into measurement. A social worker and a physician may both point to the person’s functioning as being disabling because it is restrictive or restricted. The physician is talking about the functioning of the person’s kidneys that do not effectively cleanse the poisons from the body and are thus restrictive of the body’s appropriate level of functioning (meaning the interaction of the various organ systems to maintain capacity); the social worker may be talking about the person’s fatigue (caused by the poor kidney function) that influences the person’s overall level of functioning. This functioning can be understood in terms of a person’s willful actions: how far a person can walk, whether he or she can climb steps to reach an objective, or the clarity of his or her mind to allow good decision making. One additional use of the term “functioning” involves how well the person can meet the expectations of the organization providing a job or the needs and expectations of a spouse or a child to fulfill the role of parent or spouse. This last form of functioning, at the role level, is discussed next.

The fourth conceptual element according to Nagi is the actual behavior that evolves from the circumstances in which people find themselves. This is a result of the interaction situation (shown in the adapted Nagi model and the IOM model) in which the cultural expectations of the role and the nature of the physical environment affect the person, forcing modifications in behavior in order to adjust to the situation. In Nagi’s version, the meaning of disability is “a pattern of behavior that evolves in situations of long term or continued impairments that are associated with functional limitations” (Nagi, 1965, p. 103). In some instances, the cultural expectations for a person or the barriers of the physical environment will preclude reasonable involvement in the role activity (such as working at an auto plant), and the person’s ultimate behavior is to withdraw from an impossibly difficult situation. In other instances, a person may find that personal help (either another person or an assistive device) will allow him or her to modify behavior in such a way as to continue to satisfy some of the most important elements of a role. The role is not sacrificed; it is adapted to allow for a person’s continued participation. In this instance, the flexibility of the cultural expectations and the adaptability of the physical environment, along with the level of difficulty and type of functioning difficulty the person brings to the context, combine to define the situation. Change any part of that equation and the “disability” can become more or less pronounced.

Unlike the first two diagrams, which clearly locate the unit of measurement of the concept at the person level, the location of a measure of disability needs to be at the point at which the person and cultural expectation and physical environment intersect (see Figure A-7). This cannot be accommodated in as straightforward a manner as identifying a missing leg or that a person cannot climb a set of stairs. In a survey context, if the source of information is either a person or a representative proxy and one is unable to observe the situation of the interaction, few alternatives are left. One can take a functioning approach that indicates how much difficulty a person has in a specific role situation (similar to assessing the limitation in basic actions), or one can take a behavioral approach that tries to identify how behavior has been affected by the change in functional capacity imposed by the impairment and the context.

FIGURE A-7. Disability: Located at the interaction of a person with the cultural expectations or the physical environment or both.


Disability: Located at the interaction of a person with the cultural expectations or the physical environment or both.

There is one other aspect of this process that also needs to be considered. Nordenfelt (1995, 2003) has written about ability, opportunity, and choice as the three elements associated with a person’s actions. Applied to a discussion of functioning, this would direct attention to the ability or capacity of the person to do—whether in a normative or nonnormative way—the physical, sensory, or cognitive actions called for; to be located in a place where such an action was possible and desirable; and to choose to do that action. An example may help to clarify this approach. Person A, who has limited use of the left side of her body, wants to know the weather outside. There is a window in the opposite wall from where she sits and a cane next to her chair. The person can choose to move across the room to observe the weather from the window or not. In this case, the will or lack of will of the person influences the functioning. If the limitations were different, more severe or encompassing both legs, the action would not have been possible with what was at hand. Finally, if there were no window or there was no cane available, there would have been no opportunity to accomplish the action. The choice element that Nordenfelt raises is not a consideration in any of the models, nor is it measured in current national surveys.

Purpose of Measurement

Another important background consideration related to the choice of concepts to operationalize during data collection is the purpose of the data collection, that is, what aspect of disability is the focus of concern. Because the data collected in national surveys are dictated by the orientation of the agency collecting the data—labor, health, or aging—the expertise of the agency colors and influences exactly what data are included and excluded and what aspects of the disablement process are seen as primary. When faced with making decisions about which component of a multidimensional concept is to be used to represent that concept as a data element, it is necessary to clearly understand which element of the concept is relevant to how the data are to be used (not something that is given a lot of conscious thought in many instances).

If the purpose of the data is relatively straightforward, such as the monitoring of trends in prevalence estimates of disability over time, the measurement can be relatively simple. Monitoring changes in national estimates of persons with limitations in ADLs and IADLs is an example: The data are identifying a single component of the disablement process and examining its fluctuation over a particular time or among groups. The only concern is to keep the question the same to allow for an accurate measure of trends over time. However, as my colleagues and I have noted there are multiple purposes for measurement of disability in national surveys, and that, combined with the multidimensionality of the concept, makes the development of survey questions more complicated (Altman et al., 2006). Fulfilling a specific purpose for collecting disability data may require different dimensions of the disability concept; all measures will not satisfy all uses.

In addition to monitoring trends, another purpose of disability measures in national surveys is needs assessment, covering a wide range of service provision, such as resource distribution, rehabilitation services, housing, transportation, and provision of long-term care (Altman et al., 2006). The bulk of data collection that has addressed service needs of the aging has concentrated, for example, on data about ADLs and IADLs limitations, which reflect whether the person has the ability to maintain independence and management of self-care. Prevalence estimates of those with difficulty maintaining or inability to maintain this independence in self-care have been used in analyses providing estimates of persons in immediate need of services or projecting possible future needs to influence policy decisions about long-term care. The needs assessment purpose has been a driving force in collecting disability data since disability became a formal administrative category in programs such as Social Security and vocational rehabilitation.

A new type of legislation that extends civil rights to persons with disabilities has created the necessity for a radically different approach to disability measurement. Civil rights legislation generates the requirement to monitor the equalization of opportunity of the population in question. Rather than being concerned with providing services for those most in need, this type of legislation requires that any person at risk of disability be included in the monitored population and that all types of access and social involvement be included. The focus of a contemporary civil rights perspective is located both at an activity and a participation level, to use ICF terms. However, to understand the mechanisms involved that facilitate or restrict the level of participation for an individual with impairments and concomitant functioning limitations, we must step back from measuring at the level of participation and focus on anyone who exhibits functional limitations (Madans et al., 2004). The newly proposed and tested questions in the American Community Survey (ACS; see Annex) were developed to allow for monitoring equalization of opportunity and predicated on the reasoning just discussed (Brault et al., 2007).

Operationalization of Concepts: Translation to Measures

The real challenge of measurement comes in translating the conceptual component of the model into an operational element that will accomplish the purpose of the data collection and capture the aspects of the situation that are relevant to address the issues. However, we narrow our conceptual elements when we are forced to operationalize them in the real world. Time, money, and respondent burden all limit the number of questions that can be asked and precipitate very hard choices, choices that will circumscribe full understanding of the process of disability.

Figure A-8 demonstrates what happens when one moves from the conceptual component of a model to a survey measure. Theoretical models, while abstractions of the real world that are useful for identifying the key elements and their relationships in broad-based terms without the confusion or detail of a specific empirical situation, are not practical for generating data (Altman, 2001a). They provide working and thinking space to focus on the basic ideas without getting caught up in details. However, to use the theoretical perspective, it needs to be applied to the empirical world and translated into questions that provide the data. An example of this process and how it narrows the focus of the theoretical concept would be the operationalization of the concept of functioning as identified in the Nagi and IOM models.

FIGURE A-8. Moving from concept to question using functioning as an example.


Moving from concept to question using functioning as an example.

Functioning, which can refer to any aspect of an individual’s physical, mental, or emotional actions, from walking down a road to hearing a conversation to putting dishes on a high shelf in a closet, is reduced to the number of elements about which there is space to ask. However, whatever selections are made, they come to represent that broader concept. If there is enough space to ask about a range of basic actions, such as walking, lifting, seeing, hearing, and communicating, there probably is not enough space to ask about the details of the functioning, such as how far a person can walk, or how long, whether he or she can walk up and down steps or over rough terrain or stand for long periods of time. The choices made in this circumstance define the concept as it will be measured and used in analysis, not necessarily as it has been conceived in a general model. One hopes the choices will at least reflect the needs of the data collection related to the purpose of that data collection; however, they frequently do not. If the purpose is concern about aging people’s ability to maintain their independence in the community, it is best to consider what functioning abilities are most related to that objective. An individual’s environment is another equally important facet involved in such an objective, which I discuss below.

The ICF scheme provides a useful tool to help clarify the effects of operationalization on the development of measures to examine the disability process. Consider the chapter on communication in the ICF manual as a model (World Health Organization, 2001a). In understanding the Nagi, IOM, and ICF models, we recognize that communication is an area of functioning that is important to a person’s participation in the role interactions that make up human existence. In the domain as outlined in ICF (World Health Organization, 2001a), numerous aspects of the communication process are identified, including the major components of communication, such as receiving spoken messages; receiving nonverbal messages; receiving written messages; speaking, producing nonverbal, sign language or written messages, and starting and sustaining conversation. This allows at least 9 or 10 areas through which one can operationalize the concept with the use of one or more questions, each providing a partial view of the functioning ability of the respondent in the area of communication. Each area of functioning—ambulation, using the arms and hands, hearing, seeing, learning, making decisions, and much more—would add yet another set of possible descriptive elements to be considered in the process of representing the concept. The simplicity of the theoretical definition gets lost in the specifics of the measurement potential. So although researchers may be starting from the same definition of functioning, their measurement and results may be as different as night and day.

Table A-1 shows the conceptual components of the various models, their definitions, and a selection of the operationalization possibilities. The table also indicates measurement possibilities for the various operationalizations and indicates the most commonly used measures. A comparison of the conceptual definitions and the common measures shows dramatically how far from the theoretical understanding of disability the actual measurement process brings us. By examining the information in the table, we see that not only are there many possible sources of indicators of functional limitation, disability, activity, or participation, but there are also several types or levels of measurement. The following discussion identifies those different types of measurement.

TABLE A-1. Translation of Concept to Measure.


Translation of Concept to Measure.

Types or Levels of Measurement

Figure A-9 shows the variety of levels of measurement that can provide information about disability or activities and participation, depending on the model being used by a researcher. Unlike impairment or body structure and function categories, which can be represented as present or not present and expanded by an indication of the level of severity when the problem is present, the diversity of human activity is much more difficult to capture than a physical attribute and exists at several levels of complexity. Some of the nature of that complexity is demonstrated in the figure.4

FIGURE A-9. Four types or levels of measurement. See the Annex for more detailed definitions.


Four types or levels of measurement. See the Annex for more detailed definitions.

In contrast to the measurement of impairment, which is most frequently represented in survey data by self-report of a physician’s diagnosis, there are extensive sets of questions and a variety of approaches to questions that reflect the hierarchy of complexity associated with the disability process. At least four additional levels of measurement when applied to the experience of the individual with an impairment have been elaborated (Madans et al., 2004). Using the ICF classification, Chapter 4, to provide a more concrete example of possible areas of operationalization, one gets a sense of the different levels that need to be reflected in measurement. At a very basic level, Chapter 4 provides a detailed classification of movement, in which categories are defined on the basis of movements designed to change body position or location, such as bending, standing, sitting, etc. This domain also includes categories associated with carrying objects, using the hands for grasping and propelling the body on land or in the water. Except for the last category, these activities can be conceptualized as measuring basic willful actions, or movement of bodily parts in a deliberate, intentional process to accomplish a single physical objective, such as threading a needle or traversing a room (Nordenfelt, 2003). A more complicated level of measurement that goes beyond the coordination of bodily movement in a holistic way is represented by a specific task, in which an individual is motivated to combine physical movement, intellectual activity, and the use of assistive devices in an organized process in order to reach a specific goal. So for example, an individual would use what body functions and intellectual capacity are available to him or her in order to dress to go out or to prepare a meal.

The most complicated level of mobility for an individual is involvement in an organized activity, focused on combining basic individual actions with multiple tasks in order to accomplish one or more activities associated with a specific role. It represents the completion of a combination of ongoing basic willful actions and multiple specific tasks necessary to engage in behavioral elements of an ongoing role. An identifying quality of an organized activity is that it almost always involves not only the person in question, but also negotiating interaction with other people or the management of behaviors that tacitly adhere to accepted customs of the social system that the culture has developed. Chapters 6 and 7 and, particularly, Chapters 8 and 9 of the ICF (World Health Organization, 2001a) give extensive examples of organized activities that are representations of various components of involvement through completion of complex task elements associated with various roles. The area of mobility can provide an example, in the management of a motor vehicle or the use of public transportation. Personal use of a motor vehicle requires coordination of visual and physical and cognitive actions to manipulate the machine, the necessary attention to laws about using the roadways (speed limits, stop signs, rights of way, etc.) to move the vehicle on the roadway, and geographic familiarity with the area in order to maneuver the vehicle from point A to point B. Driving a car or other vehicle is an important organized activity, because it is related to a variety of roles and may even be a central organized activity for the work role of a truck or bus driver.

Ascertaining that an individual is capable of completing a basic willful action gives no information about his or her ability to engage in an organized activity, but involvement in an organized activity does imply that the person is capable of some form of basic willful action and specific task completion, and so the levels of measurement identified here do reflect a crude hierarchy. Whether the basic actions or the tasks are carried out with the aid of assistive devices or accomplished in an unusual way (using one’s feet instead of hands) is irrelevant to the measurement of that element of participation; however, such detail may provide additional information on the person’s functioning or the environmental context.

The final level of measurement is an indication of participation in a cultural role. This can be accomplished through either a functioning approach or a behavioral approach to asking questions. A functioning approach would use indicators of limitations or inability to participate in the role, or alternatively, indicators of level of difficulty in performance of the role. An example would be a teacher who answers a question about limitations in work as limited because she can no longer stand before a classroom to lecture, but who, with the help of her employer, arranged to work with students on a one-to-one basis. Alternatively, a respondent may indicate being completely unable to fulfill certain of the main activities associated with a role. An example of this would be a teacher who has lost the ability to communicate verbally or otherwise, who can no longer interact with students in an instructive way. An alternative functional approach would have the teacher indicate the degree of difficulty experienced in performing a variety of tasks and organized activities required of the teaching role, including an indicator that it cannot be done.

A behavioral approach to participation seeks to understand changes in behavior that can be attributed to changes in capacity (or basic action functioning). Questions asked from this approach would seek to discover if a person was involved with this particular role or activity prior to the onset of the impairment or the functioning limitation and whether involvement has changed in any notable way5 (instead of answering the functioning component above as being limited, the change in the way the person teaches could be captured). In some instances, questions have sought to discover if the role behavior had increased, decreased, or remained the same (Ferron, 1981). Other approaches could identify situational changes that allowed for maintenance of the role, thus incorporating some of the environmental factors that are presently so scarce.


An examination of the large, general national surveys and the surveys directed toward the aging population shows a remarkable consistency in representations of the very different conceptual elements included. Moreover, they highlight the gaps in information collected when considered in light of all the possibilities discussed above. Tables A-2 and A-3 show the relationship of questions on disability to the theoretical concepts from current models found in general national surveys (see Table A-2) and specialty surveys on aging (see Table A-3). The following discussion examines the various representations of the theoretical concepts, the levels or types of measurement, and the specific functioning or role participation emphases included in each of the surveys; the discussion also identifies the gaps in information contained in the two sets of surveys.

TABLE A-2. Theoretical Content of Disability Questions Contained in General Social Surveys.


Theoretical Content of Disability Questions Contained in General Social Surveys.

TABLE A-3. Theoretical Content of Disability Questions Among Surveys on Aging.


Theoretical Content of Disability Questions Among Surveys on Aging.

Theoretical Concepts Represented in Survey Questions

Medical and Chronic Conditions

Although the theoretical models of disability are careful to identify and differentiate the concepts of pathology and impairments in the context of health, disease, injury, and congenital anomaly, the survey approach to identifying that element of disability consistently focuses on either identifying a specific health condition or framing questions about other conceptual areas in the context of a physical, mental, or emotional health problem. Except for some questions included in the Women’s Health and Aging Study (WHAS), the survey data represented in these tables do not allow a researcher to separate the condition-caused pathology from the impairment, nor are impairments identified, except possibly in the case of accidental injury or amputations for which some surveys indicate the location of the injury. Medical conditions serve as the catch-all for the pathology or impairment indicator and, except for the National Health and Nutrition Examination Survey (NHANES) and WHAS, in which some information is based on actual examination, responses are based on either self-reports or a self-reported indication that the condition was diagnosed by a physician. Surveys with links to administrative data—such as Medicare records in the National Health Interview Survey (NHIS) or physician follow-back for a subsample of the Medical Expenditures Panel Survey (MEPS)—can verify a diagnosis through the administrative record, but that is a factor that complicates not only the data collection process, but also the data programming task during analysis.

Conditions are most frequently collected by a bounded listing that emphasizes the most frequently occurring chronic diseases, such as heart disease, arthritis, cancer, and stroke.6 In addition, in some surveys, such as NHIS and WHAS, after being asked the questions about basic action functioning and task topics, respondents are also asked to identify the condition or conditions that are considered to be the main cause of the limitation that has been identified. Although in many cases this may be an accurate representation of the cause of impairment and functioning difficulties, particularly when only one condition is involved, respondents frequently indicate the condition occurring most closely in time to the development of the limitation, even though the limitation may be a result of an earlier condition that has worsened, or, most likely, the accumulation of conditions. Unlike the other surveys considered here, MEPS also identifies conditions in addition to those on the list that are associated with all types of medical care use, physician visits, hospitalizations, medication use, and visits to other providers. This information can serve as a check on what may be the major conditions occurring during the data collection period that may also be associated with the limitations being reported. This material is particularly useful for picking up secondary conditions that can contribute to the worsening of functional limitations, as demonstrated by Rasch and colleagues (2008).

Physical Functioning

Functioning, as identified in the Nagi and IOM models and partly identified by the activity concept of the ICF model, is represented in survey data by various versions of what some call the Nagi questions. The Nagi questions ask about physical functioning, associated primarily with movement and use of arms, legs, fingers, and the body as a whole. The original Nagi questions (Nagi, 1969), which were asked relative to a work context, were rather detailed in that they asked about lifting a series of weights ranging from 1–5 pounds to 50 pounds, asked about the left and right hands and arms separately, asked about sitting and standing, and separated the functional aspects of stooping, crouching, and kneeling. The Nagi questions found in the surveys under study are generally fewer and less specific and continue Nagi’s omission of questions related to sensory functioning. They all include at least one question about walking, and the more elaborate ones ask about the ability to walk several different distances and up steps (it appears that going down is assumed to be less difficult). Some surveys, like NHIS, ask about nine different areas of functioning, including reaching overhead with the arms, bending and stooping, using the fingers to grasp, lifting a certain amount of weight (usually about 10 pounds), and pushing or pulling furniture. Others, such as WHAS, ask about five areas of functioning, but in somewhat more depth.

Cognitive and Emotional Functioning

Other elements of functioning that the surveys attempt to capture are cognitive functioning, predominantly the ability to remember; mental health status, which is assumed to provide some insight into emotional functioning; and sensory functioning—seeing and hearing. Most of the general national surveys are limited to one question about cognitive functioning. For a short set, MEPS seems to be best because it combines three different capacities: memory loss or confusion that interferes with daily activities, problems making decisions, and requiring supervision for safety. In the other general surveys, cognitive function is equated with memory problems, while in the aging-specific surveys, various forms of Mini-Mental tests are conducted. Although those Mini-Mental tests do identify deteriorating cognitive capacity, they do not necessarily indicate how the person functions in daily activities. In the same way, the indicators of emotional functioning are generally associated with either a depression scale or a depression and anxiety measure. In some instances, questions directed at other concepts provide clues as to level of emotional functioning, such as questions in WHAS about how well a person sleeps or experiences shakiness in a particular situation. However, unlike questions that ask about the amount of difficulty a respondent has with physical movement (which gives some sense of the level of functioning), mental health questions are yes/no recitations of symptoms that probably mask the relationship of the symptom to the basic actions that would be related to emotional functioning. The actual problems created by those symptoms, such as with decision making, safety, emotional control, or withdrawal, and the level of those problems are simply assumed on the basis of the level of symptomatology. At this time, understanding of how to measure emotional functioning lags behind measurement of other capacities.

Sensory Functioning

Measurement of sensory functioning, primarily seeing and hearing, is included in all the surveys reviewed for this paper, but the adequacy of the measures to indicate functioning, even functioning potential, is poor. For example, the two questions in the Survey of Income and Program Participation (SIPP) on vision ask about difficulty seeing the words and letters in ordinary newspaper print (even when wearing glasses); at best, they only separate people who are blind or unable to see newspaper print from all others. This is useful for identifying people with severe difficulty seeing, but it does not indicate the range of difficulty or identify those who may have difficulty seeing in the distance (necessary to drive) or those with problems seeing at night, and so forth. The vision examination included in NHANES may be the one exception to this criticism, but a medical exam also does not necessarily indicate how an individual with a vision impairment is functioning in an everyday situation. Hearing questions are also insufficient in many instances, identifying those who are deaf and those who use hearing aids, but without an indicator for all others. The issue of hearing aids is also a serious complication in questions about hearing because aids do not serve to ameliorate hearing problems as well as glasses facilitate seeing.


One other area of functioning—speech—is represented only in the SIPP data. Although far fewer people experience speech difficulties than vision and hearing difficulties, it is an important area among the aging population for people who have had strokes or have conditions such as multiple sclerosis or Parkinson’s disease. WHAS is the only survey that collects data on the type of functioning problems related to hearing and speech impairments that elders experience if they have had a stroke; yet it does not collect extensive data on limitations in understanding incoming conversation, which is part of the interaction and participation equation.

Role Participation

There is a wide variety in the measurement of role participation on which the surveys collect data. In Tables A-2 and A-3, I use two columns (columns 4 and 5) to represent that area, one reflecting the behavioral interpretation of participation that comes out of the early Nagi work (Nagi, 1965) and the other reflecting the functional approaches to participation found in the IOM and ICF models. The variety I speak about above, however, is not in the role participation topics; rather, it is associated with the wording, answer categories, and selection of self-care task items in the measures. All of these surveys, particularly the aging surveys, have extensive measures of self-care tasks, the ADLs and IADLs originally identified by Katz et al. (1963). These measures focus on the ability of individuals to maintain independence in elemental self-care areas, such as bathing and dressing, and in more complicated instrumental areas, such as taking care of meals and maintaining a household. This orientation to what are important, but minimal, self-care tasks comes out of an earlier era when disability was understood as dependence and public policy addressed such dependence with various forms of care provision, including institutions. At that time, dependence, a form of nonfunctioning, was seen as an end in itself, rather than as an obstacle to participation.

Data on ADLs, in particular, are collected not only about the existence of difficulty, but also about the amount of difficulty experienced, the use of help, the need for help, and the use of assistive devices to accomplish the task. The Longitudinal Survey of Aging (LSOA), the National Long-Term Care Survey (NLTCS), and WHAS are actually quite thorough in that regard. Among the general national surveys, only SIPP has multiple questions on ADLs and IADLs; the other general surveys have fewer questions and much less detail. The aging surveys, in contrast, ask a minimum of five questions about self-care and at least five questions about instrumental activities, such as making a meal, shopping, or managing medications or money. Questions that ask about difficulties or a need for help or supervision with ADL or IADL tasks are considered to reflect a functioning approach to role participation, while questions that indicate the use of help are interpreted as indicating task behavior on the part of the respondent; they are classified in Tables A-2 and A-3 accordingly. This is the one area of disability questions that has been examined more closely and whose standardization has at least been attempted, if not accomplished (Freedman et al., 2004).

Two other kinds of questions about role participation are included in most surveys. One is about functioning in the work role (and HRS also provides extensive data on behavior in the work role), and the other is social behaviors or role functioning. The work questions refer mainly to paid employment, although sometimes to housework as well. The social role questions, usually three or four, generally ask about difficulties in social activities, such as attending church or concerts; going out to movies or sporting events; and having leisure activities, such as reading, watching television, or listening to music. A very interesting aspect of my review was the discovery of several sections of measurement that with a little tweaking would provide some very useful data on role behavior, not just functioning (these sections are italicized in Tables A-2 and A-3). An example is the set of questions about social activity in LSOA. There are eight different items that identify eight different types of current social participation. However, there is no indication of how this behavior may have changed since the onset of the functioning difficulty. Increase or decrease in the activity, as well as the addition of new activities, would provide valuable information that could document the losses or gains in participation associated with functioning problems. Other nonstandard questions already in LSOA, NLTCS, and WHAS have potential to increase data in a useful way with very little change (see the Annex for suggestions).

The one final theoretical concept about disability included in Tables A-2 and A-3 is the area of environment. Measures accounting for environmental factors all appear to be restricted to the use of assistive devices and the kind of devices in use. LSOA has some minimal information about the individual’s home, and HRS has a fairly detailed set of questions about accommodations made in the workplace by a person’s employer. The latter set could usefully be borrowed by the Current Population Survey (CPS) to address this issue for all ages.

Levels of Measurement

The dominant levels of measurement of functioning found in the surveys I reviewed are level 1 and level 2, measures of basic actions or functioning of the person and measures of specific tasks, primarily those associated with self-care and independence. Although the question included in most IADL measures on going shopping can be considered a question about organized activity, there is very little detail considered other than accomplishing the task. Except for the one set of questions about driving in NLTCS, there are really no other questions about such organized activity as using public transportation, acquiring a job, attending college, traveling to visit friends or relatives outside the local area, taking vacations, voting, and many other kinds of activity. The level of measurement of role participation is also very limited. Questions about work experience simply reflect the people’s assessment of their own ability to work, with no indication about what personal functional limitations or environmental access circumstances contribute to the answer. Information about other role involvement can be gained through answers to questions about marital status, parental status, and educational status, but little more. Questions about community roles (civic roles, such as voting or organizational membership in churches, clubs, or other groups) could well be included in surveys for the full population and would give a more rounded picture of life than is now available.


Depending on the perspective one takes, the disability data available today, with which we analyze important related policy questions, is either remarkably extensive or too narrowly conceived. Actually it is both.

Although the collection of information on impairment dates as far back as 1830 in the U.S. Census, it is a fairly recent development to have multiple questions about disability available in national databases. In 1936 the U.S. Public Health Service fielded a National Health Survey that asked about a respondent’s health and use of the health care system. A prominent component of the survey questions was the section on other handicapping disease or condition, which focused on recording all handicapping diseases or conditions for every member in the household. In addition to recording the start date of conditions and doctor use, the section allowed for collection of information about whether the condition “interferes with job” (Perrott et al., 1939). The purpose of those questions was to inform the public health sponsors about the health of the nation and the types of prevalent illnesses or diseases, as well as to identify the impairments (disabling or not disabling, although disabling was not defined). Exploration of disability other than accounting for the various conditions that caused it was beyond the purview of the survey.

In a similar fashion, NHIS, which started in 1957, had among its first publications a report on Impairments by Type, Sex, and Age (National Center for Health Statistics, 1959). The data were collected on an extensive list of impairing conditions, and prevalence rates were published. The concept of impairment was still included within illness and not explored as a precursor to “disability.”

Observing the current set of surveys from these earlier vantage points, the data available in the surveys reviewed here have broadened to encompass representation of almost all areas of the more recent conceptualizations of disability and include impressive detail about individual functioning, in most instances, as well as information about maintaining independence, using help, and maintaining social ties.

Of the two forms of surveys reviewed here, general national surveys and specialized aging surveys, each group has important strengths. Among the general national surveys, the best coverage is for the conceptual area of individual functioning. Although all areas of physical, mental, and emotional functioning are not covered (speech is one notable area missing in all but SIPP), the areas of functioning that account for most functioning limitations are covered, including difficulty walking, using arms and hands, and sensory difficulties. As mentioned above, the questions about seeing, hearing, emotional difficulties, and cognitive limitations could be improved and expanded to more directly reflect actual functioning, but there are at least representations of those functioning areas. It would be particularly useful to include additional aspects most likely to result in organized activity or role participation limitations, such as cognitive and emotional functioning, so that the relationships could be investigated. Another strength of the general surveys is that they include adult respondents of all ages, so that one can examine the continuum of disability across a wide age spectrum and possibly observe patterns of relationships that are not available in a more age-restricted sample.

Weaknesses of the data relative to theory include very limited measures of role participation and no measures of environment except for the use of assistive devices. The use of a functioning limitation approach to role participation is somewhat restrictive in that it tells us only how respondents perceive their relationship to a specific area of participation, such as limited ability or inability to work. A behavioral measure of role participation, in contrast, would be more conducive to understanding the interaction process that creates disability. It would provide an approach that captures the nature of the change in role behavior and would be more useful for measuring the social, cultural, and physical environmental elements that are related to behavior changes.

The information from the aging surveys (and SIPP to a more limited extent) about self-care tasks is particularly detailed and useful for understanding the more severe areas of deterioration associated with aging and multiple impairing conditions. It is particularly useful for estimating the need for care services for this population, since in most cases the data allow researchers to differentiate between having difficulty with self-care tasks, getting help with those tasks, and in some cases needing help with those tasks. There is somewhat greater attention to role behaviors in the aging surveys, rather than just role functioning, and several of the aging surveys have question sets that, if tweaked slightly, would provide information not only about current behavior, but also about behavior change. This would be an important clue to the disability process or the development of “disability.” One or two of these surveys do include environmental measures associated with the home setting, better than is done in the general surveys, but it is a small start in comparison to what is needed. And as with the general surveys, the aging surveys contained almost a total lack of data at the level of organized activity, which would inform about the activities in which role participation breaks down. In most instances, people do not give up social roles entirely; rather, they change the way they participate in them. Information about those activities for which there is change is useful for intervention purposes, for making things more accessible, or for encouraging greater participation. One final weakness of the aging surveys is the failure to recognize the cumulative effect of the disability process associated with aging. This process does not necessarily begin at age 65 and should be examined from an earlier point, such as 45 or 50, particularly if prevention is a goal.

Both sets of surveys have very similar data gaps. Except for the classic reference to going shopping found in IADL questions and the questions directed toward driving in NLTCS, none of these surveys provides information about organized activities associated with role participation. There are also very limited measurements of work roles and social role functioning. Given the emphasis on a functioning limitation evaluation of role participation rather than an examination of role behavior and how it might have changed since the onset of functional limitations associated with health problems, there is very little information about the disablement process. The outcome is known in a very narrow area, but the process of giving up actions or tasks as functioning deteriorates is not known, nor are the choices people make between or among role activities. As an example, people may accept help (if it is available) with ADLs and IADLs in order to have more time to engage in the tasks and activities that are meaningful to them in one or more roles. In the new conceptual orientations toward disability, the independence–dependence continuum is less important than participation and inclusion, even at the most dependent levels of functioning. There are now two policy issues related to this population: the cost and organization of care related to dependence and a mandate to facilitate inclusion and participation. The available data and research tell us very little about how to accomplish the latter, primarily because the data are not available, but also because data collection activities and research analyses are still operating under the old paradigm.

What the Measures Capture

The richness of the data available to represent the disablement process is sometimes a source of confusion to those who use the various analyses reported in government publications and journal articles. Silverstein et al. (2005) and the National Council on Disability (2008) have complained strongly about the lack of consistency of prevalence estimates from the various surveys that muddy the waters when policy issues are at stake. To a layperson who does not differentiate an ADL or IADL measure from a physical or mental functioning measure, the vast difference in prevalence estimates that are produced is confusing. Even researchers in the field sometimes inaccurately assume that persons who indicate a bathing or dressing difficulty all fall within a population estimate of persons with positive responses to the Nagi questions on functioning. Although the intuitive image of the nesting of one set of measures within the others in a hierarchical manner probably suits the broad generalizations implied by the theoretical models, the real-life examination of data does not provide such a neat package, as both Adler and I have demonstrated empirically using two different data sets (Adler, 1989; Altman, 2001a).

When examining these different measures that reflect the conceptual elements of theoretical models of disability, it is important to keep in mind that the different measures not only reflect a shorthand for the conceptual elements, but also represent different populations in the big picture of disability. The prevalence estimates and percentages in Table A-4, taken from a recent chartbook about disability and health, show those striking differences. Taken together, the combined measures of disability available in NHIS identify more than 66 million adults or 31.4 percent of the noninstitutionalized adult population. By far the greatest proportion of that population, more than 62 million or (29.5 percent) were identified by responses to questions about basic action functioning (physical, sensory, cognitive, and emotional); almost 46 million (21.7 percent) indicated some difficulty with the physical functions represented by the Nagi questions. Basic action difficulties represent other areas of functioning as well: 27.6 million (13.1 percent) indicate sensory difficulties; 6.5 million (3.1 percent) indicate emotional difficulties; and 5.9 million (2.8 percent) have cognitive problems, at least with memory and confusion. These total only 62 million because almost 19 million have limitations in more than one area of functioning.

TABLE A-4. Population Estimates Based on Concepts Used to Measure Disability, Total Adult Population, and Population Ages 65 and Over.


Population Estimates Based on Concepts Used to Measure Disability, Total Adult Population, and Population Ages 65 and Over.

A little less than half of the total population identified by limitations in basic actions were identified by the other commonly used measures, task or role limitation: 30 million (14.3 percent) reported a limitation in self-care, work, or social roles. Within the group with role limitations, 24.5 million (11.6 percent) reported work limitations; 14.6 million (6.9 percent) reported social role limitation, and 8.7 million (4.1 percent) reported difficulties with ADLs or IADLs or both (Altman and Bernstein, 2008). It is not surprising that policy makers and the public are confused.

Which is the real population with disabilities? Each data point can trace its origin to a conceptual component in current theoretical models, but the concepts represent different aspects of the disablement process, and the measures represent different aspects of the concepts. Researchers who have fixed their approach to disability at the level of ADLs and IADLs would probably argue that this area of focus reflects the most important health and health care issues: this is the group that needs help, this is the group that displays the most disability by displacing a greater part of the mat—from the IOM model (see Figure A-3). However, for those who work from a civil rights perspective and are attuned to the underlying intent of the Americans with Disabilities Act to make inclusion and participation available to this population, the population who are “at risk” to develop a disability because of the interaction of their functional limitation and the cultural and physical environment is the real population. It is not my place to say which measure is best, because they all serve a purpose. However, I note that the use of any one measure to the exclusion of the others distorts understanding of the total process; the coordination of the number of questions, the functions included, question wording, answer categories, and conceptual elements across surveys would help improve the confusion about numbers. And because the gaps in information are great, as demonstrated by Tables A-2 and A-3, efforts to fill those gaps would go a long way toward understanding the whole disablement process, whether the focus is a subpopulation of adults or the whole population.

How the Data Are Used

Finally, the information in Table A-5 provides a window on how the conceptual elements that are measured inform understanding of disability among the elderly. Using two journals from the past 3 years, Demography and the Journal of Gerontology, articles that used a disability measure (broadly defined) in the analyses were selected in a random manner. Table A-5 shows the article reference, the data source, the primary and secondary disability measures, and a very brief indication of how the measures were used. A total of 11 of the data sources were large national surveys, 10 in the United States and 1 from Japan. The single most frequently cited data set used was HRS, with NHIS a close second. It is interesting to note that the 1994–1995 NHIS-D accounted for most of the articles that had the NHIS as a data source.

TABLE A-5. Sampling of Disability Measures and How They Are Used: Demography and the Journal of Gerontology.


Sampling of Disability Measures and How They Are Used: Demography and the Journal of Gerontology.

The predominant conceptual measure used in 13 of 18 articles was a measure of ADLs and IADLs, some using a functioning perspective about difficulty and others using a behavioral perspective about receiving help. Although the conceptual base is similar, the measures vary not only by the difference between a behavioral or functional approach, but also by the number of questions involved. So, for example, the Freedman and colleagues (2007) and the Mutchler and colleagues (2007) articles use two questions, from two different data sources, to represent ADLs and IADLs (one for each concept), whereas Liang and colleagues (2008) use 11 questions to represent the ADL-IADL construct. For the remaining articles that do not use an ADL-IADL construct to represent disability, one uses a work limitation question, one uses a summed indicator of limitations in eight basic actions (also known as Nagi questions), and the final one uses the short form SF-367 on physical functioning and pain. This concentration of measures in a very narrow area of the disablement process reflects a very limited orientation toward disability in this population. In addition, if one were to compare the populations described in each of these articles to one another, as in Table A-4, chances are the overlap would not be extensive, nor would it be consistent.

Nine of these articles use the measure of disability as a dependent variable, and several use it to map trends in prevalence over a time period. Trends that are followed include the need for help, life expectancy, active life expectancy, and transition into and out of a disabled status (disabled status being equated with high levels of dependence). The other nine articles use the measure of disability as an independent or control variable to predict other things, such as how long baby boomers are expected to work, the risk of nursing home admission, the use of assistive devices, physical activity, and weight changes. In a few instances, there are indications of either a lack of familiarity with the current theoretical models of disability or lack of understanding of the value of some of the measures that are available to be used. The first problem can be found in several of the articles in the use of terminology to discuss disability aspects of the analysis. A common terminology still is not being used and in some cases the conceptual elements of theoretical disability models (identifying functioning difficulty as impairment) are being confused.

Another problem is the continued restrictive interpretation of disability measures available for use and the lack of appreciation of broader aspects of disability (as conceptualized beyond the dependence focus that has been demonstrated here and inclusive of environmental factors when available). An example is the Mermin and colleagues (2007) article, which examines predictors of the length of time baby boomers feel they will work before retirement. HRS is used and an indicator of work limitation is one of the independent variables. It is a routine assumption that persons with work limitations will not work as long as persons without work limitations. However, there are available data in HRS that could have been used to test this routine assumption. HRS has a series of 10 questions that indicate if and how an employer has provided help so that a worker can stay on the job. If that information had been factored into the analysis, it could have given some insight into the effect of environmental factors on disability behavior associated with retirement and provided a very meaningful comparison related to retirement choices.

As with the examination of the data elements of the commonly used surveys in Tables A-2 and A-3, the literature reviewed hints at an even narrower use of the data for research purposes. Available environmental elements are used in only one of the articles, and that article focuses on tracking the use of assistive devices. The various role participation representations were used in only 1 of the 18 analyses. The broad emphasis of the literature seems to be descriptive of the status of dependence, either documenting changes in the prevalence of the disability variable over time or the effect of various other statuses—immigrant, age, race, gender—on prevalence of dependence (as represented by the ADL-IADL measures). Of course, using such a small sample of articles from only two journals provides very little data on which to make a fully accurate assessment.


Although there are some very useful theoretical models of disability to underpin a wide-ranging research agenda about disability, the measurement of the conceptual components in the existing data sets and the use of data already available have not yet reached their potential. In some instances, the data and the analyses are still too closely tied to the medical conceptualization of disability, as a problem located within the individual. In other instances, the reduced financing and increased demand on data collection processes have forced choices that limit the expansion of the conceptual coverage of the data. Integral components of the disability process, elements of role participation, and the interaction of the individual and the environment are vital to a more complete understanding of disability, but they are not generally considered.

Although groups at various universities are working on some of these measurement problems, there is no general funded mandate, particularly in government-sponsored data collection efforts, to test or expand disability measurement beyond what is currently in use. Nor, until this year, has there been any coordination across data collection entities to consider some form of standardization of core efforts. A recent hearing in the U.S. House of Representatives (in June 2009), held in response to the National Council on Disability (2008) publication about disability data, may have drawn some more serious attention to this issue. The testing and approval of the ACS disability questions and their adoption for use in CPS, in the National Crime Victimization Survey for the Department of Justice, and for testing in NHIS may foretell the eventual closer coordination of disability measures, if not their immediate expansion.

Jette and Badley (2002, p. 183) have noted that 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.” I strongly agree and would add that the field also needs some expansion of measurement to cover all the conceptual components of our theories, as well as coordination of measures that represent those theoretical concepts. A very careful consideration of the use and interpretation of measures, particularly in research that is used to inform policy, is critically necessary. Whatever uniformity is developed in conceptualization and language is still undermined when it is not used in creating operationalized definitions of concepts and there are multiple variations in question-and-answer language.

The strong medical model basis of work on disability in gerontology has created a rich set of measures that are narrowly focused in the area of identifying behavioral and functioning dependence. The measures have provided important policy information about problems and cost of the final one-eighth to one-tenth of the life-cycle. The data based on those measures have documented changes in longevity and health in people’s final years and have provided information that has allowed for the development of assistance programs that go beyond warehousing our elders in institutions. However, the very data and forms of measurement that have helped identify and understand the change in the structure of the problems of the aging population are no longer sufficient to address all the issues, particularly in relation to role participation. A 65-year-old person who is facing the very likely possibility of another 20 years of life may also experience the role changes associated with gradual development of functional limitations in basic actions before reaching the stage of dependence. Understanding the issues associated with the organized activities that are key to maintaining role participation, including the role that society and environment play in the process, can go a long way to improving those 20 years, as well as the final period of dependence.

Finally, it is interesting that while none of the models currently in use proposes differentiating the meaning of disability among the three major age groups—children, adults, and the elderly—we go about measuring disability within those groups in very different ways. Children’s disability is measured using either conditions or use of special services; adults’ disability is measured most broadly through a combination of functioning in basic actions, limitations in work, and ADLs and IADLs, with an emphasis on work limitation; and the aging population’s disability is represented most commonly by behavioral or functioning representations of ADLs and IADLs or, somewhat less frequently, by levels of functioning in basic actions.

Ferraro (2006, p. S3) has made the point that “gerontology flirts with being medicalized” and should investigate topics not directly related to health. Studying the problems of disability from a role participation perspective would move away from that health focus and contribute to the overall understanding of the aging process over the life-cycle. Expanding survey measurement to include a fuller, more robust coverage of functioning in basic actions, indicators of organized activity participation meaningful to role participation, and measures of key environmental factors would facilitate the study of disability across all age groups.


American Community Survey Questions8

Answer question 16 ONLY IF this person is 1 year old or older. Otherwise skip to the questions for person 2 on page 12.

  • 16. a. Is this person deaf or does he/she have serious difficulty hearing? YES/NO
  • b. Is this person blind or does he/she have serious difficulty seeing even when wearing glasses? YES/NO

Answer question 17a ONLY IF this person is 5 years old or older. Otherwise, skip to the questions for person 2 on page 12.

  • 17. a. Because of a physical, mental, or emotional condition, does this person have serious difficulty concentrating, remembering, or making decisions? YES/NO
  • b. Does this person have serious difficulty walking or climbing stairs? YES/NO
  • c. Does this person have difficulty dressing or bathing? YES/NO

Answer 18 ONLY IF this person is 15 years old or older. Otherwise skip to the questions for person 2 on page 12.

  • 18. Because of a physical, mental, or emotional condition, does this person have difficulty doing errands alone such as visiting a doctor’s office or shopping?

Definition of Terms

Willful action—Based on either performance or capacity, action reflects the individual’s will to carry out basic volitional bodily operations at the level of the organism (whole person). Examples include walking, climbing steps, reading, communicating, etc. It is distinct from body functions (ICF), which are “physiological functions of body systems” rather than functions of the whole person. When combined, multiple actions can result in performance of tasks (Nordenfelt, 2003). In the ICF, actions are included in the domain of activity defined as “the execution of a task or action by an individual, representing the individual perspective of functioning” (World Health Organization, 2001b, p. 190). ICF does not differentiate actions and tasks.

Specific task—Execution of a group of willful actions by an individual. It is an indicator of a series of related or more complicated actions necessary to accomplish an objective, which is a central component of role behavior. Examples include bathing, dressing, and feeding, which are central elements of self-care, or driving a car and planning a meeting, which can be central elements of employment. In ICF, tasks are included in the domain of activity defined as “the execution of a task or action by an individual, representing the individual perspective of functioning” (World Health Organization, 1991b, p. 190). ICF does not differentiate actions and tasks.

Organized activity—Represents the accomplishment of a variety of specific tasks and willful actions in order to complete an activity that is socially recognized or defined in a culture. An example would be going out to dinner, which entails making reservations, getting dressed appropriately, finding transportation, engaging with friends, reading a menu, ordering, paying the bill, leaving a tip, and other details.

Role participation—Represents the accomplishment, through willful actions, specific tasks and organized activities, of enough elements of a social role to claim that form of role participation as represented in a particular culture or society.

Current Questions and Suggested Additions

National Health and Nutrition Examination Survey

In a typical week, how many times do you talk on the telephone with family, friends or neighbors?

How often do you get together with friends or relatives; I mean things like going out together or visiting in each other’s homes? (per year)

About how often do you visit with any of your neighbors, either in their homes or in your own?

How often do you attend church or religious services?

Do you belong to any clubs or organizations such as church groups, unions, fraternal or athletic groups, or school groups?

Altogether how often do you attend meetings of the clubs or organizations to which you belong?

Suggested additions to monitor behavioral changes would include some measurement of how this behavior differs from that which occurred before the onset of the limitation. It would require tracking of what has been reported as limitations in functioning or tasks or organized activities.

An example would be additions to the following questions to track those changes:

Do you belong to any clubs or organizations such as church groups, unions, fraternal or athletic groups, or school groups?

Have your group memberships increased, decreased, or remained the same since the onset of [fill in with type of functional limitation, i.e., your experience of limitation in walking—various ways to include limitations in different areas of physical functioning can be developed]?

Altogether how often do you attend meetings of the clubs or organizations to which you belong?

Has your meeting attendance increased, decreased, or remained the same since the onset of [fill in with type of functional limitation, i.e., your experience of limitation in walking]?

Next, depending on the answer provided (increase, decrease, or remained the same) a follow-up could probe why the behavior changed (increased or decreased) with no questions if it stayed the same.

Longitudinal Study of Aging

During the past two weeks, did you—

Get together socially with friends or neighbors?

Talk with friends or neighbors on the telephone?

Get together with ANY relatives not including those living with you?

Go to church, temple or another place of worship for the services or other activities?

Go to a show or movie, sports event, club meeting, class or other group event?

Go out to eat at a restaurant?

Do unpaid volunteer work, such as teaching, coaching, office work, or providing care?

Participate in Elderhostel?

Suggested additions would be similar to those suggested above. The operative element being to discover if this activity represents a change from the activity level or type of activity experienced before the functional limitations began to be noticeable.

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The author gratefully acknowledges the meaningful input on conceptualization, organization, and editing provided by Julie Weeks of the National Center for Health Statistics of the Centers for Disease Control and Prevention.


This is an example of how disciplinary language and orientations impose subtlely but importantly on a conversation of this type. Nagi is a sociologist, and his work reflects a sociological orientation to culture and social roles. The general term social role (or simply role) is used to refer to both a position and its associated behavioral expectations. The role of a person with a functional limitation as understood through the behavioral expectations of the group of which they are a part is a key factor in creating disability.


From the author’s perspective it also takes the process out of the medical context so important for the individual’s health but separate from the social construction of disability that results through interpersonal, organizational, and social activities (Bogdan and Biklen, 1977).


Role set refers to the persons most commonly found to interact with an individual in specific role situations, so in the family situation the role set includes a spouse and children or parents, whereas in an employment situation a role set includes employers and colleagues or coworkers.


See the Annex for definitions.


The Social Security Administration used questions of this nature in a series of surveys in 1972 and 1974. They combined to provide a scale that very effectively represented the net result of having an impairment and functional limitation in terms of participation at the time of the survey (Altman, 1984).


On the MEPS and the Health and Retirement Study (HRS), see the health status sections for examples of the conditions considered important to capture.


The SF-36 is a comprehensive short form of a health survey, developed by John Ware, with only 36 questions that yields an eight-scale health profile as well as summary measures of health-related quality of life. For more information, see http://www​


This section is excerpted from the full ACS questionnaire, which is available at http://www​​/acs/www/Downloads/SQuest09.pdf.

Copyright © 2009, National Academy of Sciences.
Bookshelf ID: NBK28474


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