Annals of Epidemiology 24 (2014) 2e7
Contents lists available at ScienceDirect
Annals of Epidemiology journal homepage: www.annalsofepidemiology.org
Disability symposium
Definitions, concepts, and measures of disability Barbara M. Altman PhD * Disability Statistics Consultant, Rockville, MD
a r t i c l e i n f o
a b s t r a c t
Article history: Received 24 September 2012 Accepted 3 May 2013 Available online 29 October 2013
The term “disability” is a shorthand expression or as explained in the International Classification of Functioning, Disability and Health an umbrella term. It has been used to identify the impairments that result from disease and injury, the physical, and mental or emotional functional limitations or difficulties a person has as a result of the impairments, as well as the participation restriction they experience when the environment is not supportive. Thus the term disability has been used to represent almost any of the conceptual components associated along the ability continuum that impacts the person, but it also includes the environmental effects that create a limiting impact from the context outside the person. This paper examines those concepts and definitions to provide insight into the measurement process to represent this important element of health and participation. Ó 2014 Elsevier Inc. All rights reserved.
Keywords: Disability Definitions Measurement Measurement purpose
Introduction On the basis of the current theoretical and legislative models of disability, there is general agreement that given the person’s level of physical, mental, or emotional functioning, the disablement process is associated with the nature of the interaction a person has with all aspects of his or her environment. That in turn can affect the level of social participation the person experiences. This paper briefly describes the conceptualization of the disability process as it proceeds from medical condition to restricted participation, and identifies the best way to measure the phenomenon for policy research use. Although disability can be attributed to the impairment or physical/mental outcome caused by a medical condition, it is also a social construct that results from the social and physical environment in which a person lives their life. Therefore, it is necessary to examine the complete process associated with the development of disability. The disability process, which may start with a disease, birth defect, or accident also includes the personal and environmental characteristics associated with the individual and although it contains numerous elements, the general nature of the process is fairly straightforward. The physical, mental, or emotional condition (disease or active pathology, injury, or congenital accident) that afflicts a person does (or does not) create an active physical, mental or emotional impairment in the cellular, organ, or limb levels of the individual in the active stage of the disease. When the acute phase * Corresponding author. Disability Statistics Consultant 14608 Melinda Lane Rockville, MD 20853. Tel: 301-460-5963. E-mail address: [email protected]. 1047-2797/$ e see front matter Ó 2014 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.annepidem.2013.05.018
of the disease, injury, or birth defect is completed, a residual impairment (abnormalities or losses that remain after the active disease pathology has been arrested or eliminated) can remain. The residual impairment also at the cellular, organ, or limb level can in some way change the capacity of those cells, that organ, or a limb so that they work differently than before the condition began. The residual impairment can create some physical, mental, or emotional functioning difficulties when the person attempts to act willfully. It can manifest as simply as creating a limp when walking across the room or with more complexity as when a person shuts down cognitively when in a stressful situation. These are examples of the possible functional limitations or difficulties a person brings to carrying on their life after disease, injury, or congenital accident. Whatever the functional limitation that is produced, it becomes a characteristic of the person, one of many. The impact of that functional limitation when the person interacts in their environment can be a risk factor for further limitation that is created by the receptivity or lack of receptivity of that environment to the specific type of functional limitation. Figure 1 provides a visual model of this process. The term “disability” has become a shorthand expression or an umbrella term that is used to represent the variety of the different aspects of the disability process [1]. It has been used to identify the active or residual impairments that result from disease and injury, as well as the physical, mental, or emotional functional limitations or difficulties a person has as a result of the residual impairments (as described), and also the participation restriction the person experiences when the environment is not supportive. So the term disability has been used to represent almost all of the conceptual components along the diseaseedisability continuum that impacts
B.M. Altman / Annals of Epidemiology 24 (2014) 2e7
Fig. 1. Visual model of elements of disability process and their relationship [4].
the person, and it also is used to represent the results of the environmental effects that create a restriction or barrier outside of the person. As such, it has become a word almost without meaning, because it has been used to represent so many different aspects of the process. The term has been associated not only with different elements of the disability process, but also within the different time frames associated with the elements of the disability process. Additionally, it is used in a generalized way rather than with a specific orientation. So, for example, when used to represent functioning difficulties it indicates the point on the functional continuum at which the person exhibits a recognizable difference of reduced functional capacity/or performance from others or from the person’s own previous capacity or performance. However, this point is also linked to both the type of social roles in which a person participates and the physical and social environment in which they attempt to play those roles. Therefore the ‘disability’ may change or fluctuate based on the conceptual component focused on and the specifics of the individual’s characteristics (age, gender, race) and circumstances. When represented in measurement at the person level it may reflect general personal capacity but when represented in measurement by participation, it may also include numerous elements of participation role requirements and of the environmental context. From a social or policy perspective, we are concerned about identifying these environmental and personal elements so that we can provide social policy, education, or changes to improve the individual’s ability to enact their roles. Definition and measurement of disability then become important tools for improvement. However, a complicating factor in definition and measurement is that there is not a clearly marked separation between those with disabilities and those without disability. Although we try to treat disability as a dichotomous situationdeither a person is disabled or notdit is not the reality. People may be disabled in one situation and not another, depending on what is required of them, what the environmental conditions are, or what the purpose or objective of the definition used to describe the situation. Except for persons with very severe limitations who would be identified as disabled on any type of measurement scale, prevalence estimates of disability are subject to the basis of the measurement (what types of limitations, or activities are the point of focus) the person’s environmental situation at the point/time of measurement (is the weather, building structure, lighting or many other characteristics of the environment supportive or restrictive?) and the intent or purpose for which the estimate is required (are we attempting to ascertain the number of persons who will need fiscal support because they can’t work or are we identifying a group whose civil rights to access may be restricted or prevented?). This
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latter requirement is what forces us to create a dichotomy for policy purposes. However, the dichotomy is very different depending on the nature of the population defined by the analytic or policy purpose we are trying to measure. Examples of some of the many purposes for which we make disability prevalence estimates are numerous, but 2 very different general examples are most common. Civil rights purposes seek to impact on a broadly defined group, anyone with a disability; while benefit programs are organized for specific groups defined by their age, location or a specific characteristic or a specific condition or impairment. Different purposes use different definitions of disability, which highlight different conceptual elements and focus the measurement process on those highlighted elements. In large national surveys, it is much easier to identify and collect data on a generalized measure of functioning, such as mobility impairment, which can occur in a large number of condition and injury specific circumstances, than to collect information that accurately identifies specific diagnostic conditions so that the individual conditions are represented with a minimum of error. This means that national survey data are better suited to fulfilling a more generalized purpose, such as civil rights, than multiple more specific purposes linked with narrow programmatic definitions of the population to be served. Variety of Disability Definitions The Americans with Disabilities Act focuses on a civil rights purpose to promote the equalization of opportunities for all persons with disabilities. Based on the Equal Employment Opportunity Commission and the Department of Justice Americans with Disabilities Act Handbook, it includes both a focus on physical, mental, emotional functioning or some specific impairment that substantially limit functional actions, as well as related major life activities. It includes everything from breathing to participation in social life. A variety of enforcement areas are noted in the act, including equal employment opportunity and nondiscrimination in state and local government services, and the definition of disability which is encompassed is by far the broadest of all those found in federal legislation [2]. Social Security Disability Insurance represents a specific benefits program that provides income for workers whose disability is substantial enough to preclude employment. The definition includes a major focus on medical diagnosis (to substantiate the severity of the condition and associated limitation) and the demonstration of the inability to work. Thus, as with many other specific disability programs such as those directed at persons with intellectual and developmental disabilities, the definition of the qualifying population is more limited and, in the case of Social Security Disability Insurance, includes the types of conditions, the level of severity of the diagnoses, and the additional need to demonstrate an inability to work. A public health focus on disability is included in a wide range of legislation, but is not always separated as a unique category. It can either be inclusive of the broad population that experiences functional limitations in any area of action for concerns such as disparities in access to health care or evaluation of the overall costs to maintain health among this population, or it can be more narrowly focused on only those whose functional difficulties that create limitations in complex activities required to participate in the community. It can also focus on a subpopulation within the larger general population with disabilities either based on a specific type of functional limitation, such as mobility or cognitive limitations, a specific type of participation restriction such as difficulty maintaining self care independence, or, based on particular programmatic requirements, on a specific diagnosis such as autism or spinal cord
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injury. However, focus on a subgroup should not and cannot be generalized to the full population. Translating definition to measurement These three different orientations to purpose generate different specific aspects of the definitions which in turn highlight different components of the disablement process. Measurement, which tries to operationalize the specific conceptual element in a definition, will then come up with a variety of approaches to translating the specific conceptual element into real-world experiences and thus our estimates will vary and our measures may not even capture the same people. Each measure, which in a survey usually takes the form of a question or a series of questions, can only approximate a part of the population we seek, because a question can only generally tap one topic such as having difficulty walking or being unable to bathe or dress oneself. Definitions (legislative and other) are important for creating the focus, but measurement creates the data we use for analysis of all the questions we want to answer. Measurement of the various conceptual components can overlap, but cannot necessarily be used interchangeably. Measurement, not definition, provides our understanding of the outcomes of programs and identifies the service gaps. How do we find a real, everyday experience to represent the concepts we have chosen to identify as “disability”? If we focus on diagnosed medical conditions, we run into error because not everyone has a diagnosis or because the diagnosis can represent a wide range of disabling characteristics the individual may or may not exhibit. Take a diagnosis of diabetes. The person with diabetes may have several problems that create a disability, such as limited vision or an amputation. However, the person with a diabetes diagnosis can also have a well-controlled disease state without any physical, mental, or emotional limitations that influence their interaction in the environment. Should we really consider the latter person as disabled? If we choose to use a medical diagnosis as our indicator, we are at least separating those who have the potential to develop the functioning limitation or social participation restrictions associated with disability from those who for the moment have none. They may or may not experience residual impairment, and that can be followed by possible participation restriction. However, if we focus only on the actual physical, mental, or emotional limitations in functioning that results from residual impairments caused by the original disease state, we capture a more reasonable representation of the population that is at risk (with a greater potential) of participation restrictions depending on the environment in which they attempt that participation. The more elements of physical, mental, or emotional functioning we can include in the question sets the more likely we identify the majority of persons who will experience the disabling outcome that environments can create (one of the nice things about focusing on limitations in physical, mental, or emotional functioning is that we have a smaller potential group of items to include than the disease listings in the 9th edition of the International Classification of Diseases). Because the science has not yet identified valid and reliable measures of environments that limit participation, the closest we can come to identifying the population that has the potential to be limited in participation is to identify those with functional limitations that may or may not be accommodated environmentally. These are the persons we identify as being at risk, but whose outcomes are uncertain without the environmental component of the measurement, which should include not only the physical environmental barriers, but also those associated with attitudes of others. The person’s functional difficulties or limitations can put them at risk to experience disability, but it is the environmental (social and
physical) context that actually creates the level of participation restriction one experiences. There are two commonly used general measures in federal surveys todaydone that identifies the most commonly found functional difficulties or limitations and reflects the individual’s physical, mental and emotional functioning status as the whole person initiates willful activity. And twodbecause we cannot yet efficiently measure environment, we measure restricted participation which we assume results from some manner of environmental problems or barriers as the person performs their daily activities. These reflect the attempts at more complex activities, such as maintaining independence, working, and participating in social activities. The first form of measurement identifies, at the person level, limitations that, depending on environmental context, can be associated with participation limitation. The second form of measurement only identifies those who experience participation restrictions in their current settings and leaves out those who may experience participation restrictions in the event of transportation changes; movement to new, less supportive environments; or reductions in support funding. It is best not to identify disability based on health condition because not all people with health conditions experience functional limitation and not all people with functional limitations have necessarily been diagnosed with a medical condition. However, although we do not want to include fully functioning individuals in a measure of disability based just on a condition diagnosis, do we want to leave out of a count those with identified functioning issues who for the particular moment are able to participate in their present environment. In the latter case, the uncertainty factor is strong, especially in emergency type situations and in periods of financial uncertainty. For the most part, the measures discussed have been applied to adult populations. Measuring disability is a more complicated process among children, particularly young children, and those measures at this point in time focus on either special education attendance or medical diagnosis and have not evolved as the measures for adults have. Examples Using the National Health Interview Surveydone of the richest surveys in terms of disability measuresdthe next two figures provide examples of the two primary types of measurement sets and the possible uses of each [3]. The first type is located at the individual level and represents the person’s physical, mental, or emotional functioning capacity or performance. Figure 2 shows the measures in basic actions which represent these functioning difficulties. There are four components of the measures of basic actions: (1) Movement difficulty measures that capture the physical
Fig. 2. Percentage of adult population with functional difficulties in basic actions.
B.M. Altman / Annals of Epidemiology 24 (2014) 2e7
Fig. 3. Percentages of adult population with participation limitations in complex activities.
limitations in moving arms, legs, fingers and body based on the level of difficulty the individual reports with walking, standing, sitting, grasping, etc.; (2) measures of sensory function including having difficulty or being unable to see or hear; (3) measures of cognitive functioning which focuses on remembering and concentrating; and (4) a measure of emotional functioning primarily based on level of feelings that could be associated with anxiety and/or depression based on the Kessler scale (more in-depth detail about the measures are provided in the Appendix). Functioning areas associated with communication, learning, and some areas of cognitive functioning are not yet well-represented by questions that have been developed and tested for survey use. These measures show that the four types of basic action measures taken altogether reveal that 29.5% of the adult population (approximately 62.3 million), ages 18 and over, indicate a difficulty in at least one area of physical, mental, or emotional functioning and can be considered at risk to develop a disability depending on the environment in which they act. The greatest proportion indicate a movement difficulty, 21.7%, whereas 13.1% report sensory functioning limitations, 3.1% report emotional difficulties, and 2.8% indicate cognitive functioning difficulties. Approximately 30.3% of the population with a basic action difficulty have difficulty with more than one area of functioning (more in depth detail about the data can be found by reviewing the reference at the website provided [3]). The second type of measure is related to activity located at the intersection of person with their environment and reflects their experience in that environment by indicating that either their participation/activities have been facilitated (they are involved in the activity) or restricted (they have some difficulty or cannot do the activity). In this instance, approximately 30.1 million persons indicate complex activity limitations associated with participation (Fig. 3). Participation restrictions can be caused by the severity of the person’s basic action difficulties, but it also can result from little to no accommodation, no assistive devices, or discriminatory actions in the environment; thus, not all disability reflected in a participation restriction measure is necessarily directly proportional to the individual’s difficulties or the severity of their health conditions. Approximately 14.3% of the adults 18 and over reported a limitation in some form of complex activity. The largest area of complex activity difficulty is the work area where 11.6% indicate they are limited or unable to work. Only 4.1% indicate difficulties with maintaining independence (based on activities of daily living or instrumental activities of daily living) and 6.9% have difficulties participating in leisure type activities [3]. As we commonly find, fewer than half of the persons who experience functional difficulties in basic actions in the National Health Information System (NHIS) data (Fig. 2) also indicate that they
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experience limitations in one or more of the measured complex activities (41.9% exactly) [3]. It should be noted that, although we have focused on two populationsdone with basic action difficulties and the second with complex activity limitationsdthese measures are a construct of several groups of questions representing various components of the disability process. In the first instance, basic action combines functional limitation characteristics of the individual and provides a person-level measure. In the second instance, the complex activity limitations combine to give us a representation of the person’s ability to participate within their environment. As indicated, the combination of the measures is what gives us our general prevalence estimates (either at the person level indicating risk of disability or at the participation level indication possible environmental restrictions). However, based on the research question, use of only one of those components of these general measures may be a reasonable use of the data. However, it should be kept in mind that movement difficulty does not represent the total population with basic action difficulty, nor does work limitation represent the total population with limitation in complex activities, only the largest component within that group. In addition, there is not complete overlap between persons with basic action difficulties and persons who report limitation in complex activities. About 3% of persons with complex activity limitations do not report any of the basic action difficulties measured in the NHIS data. The expectation is that they have difficulties with other basic actions that are not measured in the NHIS survey, such as learning difficulties, emotional problems not captured, or pain and fatigue that at the time of this data collection was not measured.
Conclusion Many who look at measurement today do not see any change or coming together of our approaches to measuring this population. But having studied the beginning of measurement in the US Census, starting with the two questions used in 1830 about being either deaf or blind, I do see movement toward a more coordinated approach. I would make several points to indicate the basis for that feeling. First, after 12 years of work, the international community, through the work of the Washington City Group, has come together on a set of six questions for use primarily in censuses. Approximately 30 counties used those questions in this recent round of censuses allowing for the very first time cross country comparisons based on the same questions. Those six questions reflect the most commonly occurring functional difficulties and some basic activities of daily living and instrumental activities of daily living. Second, the American Community Survey questions on disability that have successfully been implemented not only in the American Community Survey, but also in a variety of federal surveys, including the NHIS, the Current Population Survey, the Survey of Income and Program Participation, and the Crime Victimization Survey are very similar to what has been accepted by the international community. The American Community Survey questions, as a function of the role of census, provide a standard measure identifying this population for any number of program apportionments. Equally important the questions are providing our first standardization of disability measurement that has ever occurred across federal surveys and have been accepted as the basic measures to be used for the purposes of the new health care act. Finally, the future looks promising as well. Because the important intervention point to reduce or modify disability is with the environment, that is an area we must measure and address. There are several environmental measurement projects under way and it
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B.M. Altman / Annals of Epidemiology 24 (2014) 2e7
is just a matter of time before we have a reasonable set of questions to add to our surveys. The toughest problem is improving our measures of mental health functioning, incorporating more rare types of functioning limitations and adding areas such as pain and fatigue, which are important areas of difficulty for many individuals. Work in those areas are in the early stages.
References [1] World Health Organization. International classification of functioning, disability and health. Geneva, Switzerland: World Health Organization; 2001. [2] Americans with Disabilities Act of 1990 (ADA). P.L. 101-336 (July 26, 1990). Title 42 U.S.C. 12101 et seq. U.S. Statutes at Large, 104, 327e378. [3] Altman B,, Bernstein A. Disability and health in the United States, 2001-2005. Hyattsville, MD: National Center for Health Statistics; 2008. http://www.cdc. gov/nchs/data/misc/disability2001-2005.pdf. [4] Altman, B. Another perspective: capturing the working-age population with disabilities in survey measures, Journal of Disability Policy Studies http://dps. sagepub.com/content/early/2013/01/31/1044207312474309; February 4, 2013.
Appendix. Measurement of variables in Figures 1 and 21 Complex activity limitation Self-care limitation The self-care measure is based on National Health Information System (NHIS) questions on whether a person had difficulty with any component of either the activities of daily living (ADL) index or the instrumental activities of daily living (IADL) index, which are defined here: ADL are activities related to personal care and include bathing or showering, dressing, getting in or out of bed or a chair, using the toilet, and eating and getting around inside the home. In NHIS, respondents are asked whether they or family members 3 years of age and over need the help of another person with personal care because of a physical, mental, or emotional problem. People are considered to have an ADL limitation in NHIS if they respond affirmatively to the ADL questions and if the condition causing the respondent to need help with the specific activities is chronic (based on permanent chronic conditions such as diabetes or indications that the condition has existed for 3 months or more). IADL are activities related to independent living and include household chores, doing necessary business, shopping, or getting around for other purposes. In NHIS, respondents are asked whether they or family members 18 years of age and over need the help of another person for handling routine IADL needs because of a physical, mental, or emotional problem. People are considered to have an IADL limitation in NHIS if they respond affirmatively to the IADL questions and if the condition causing the respondent to need help is categorized as chronic (based on permanent chronic conditions such as diabetes or indications that the condition has existed for 3 months or more). Social limitation Social limitation is defined on the basis of three NHIS questions: “By yourself, and without using any special equipment, how difficult is it for you to .Go out to things like shopping, movies, or sporting events?
1 It should be noted that questions on pain and fatigue were added to the NHIS in 2011, after this material was originally presented.
.Participate in social activities such as visiting friends, attending clubs and meetings, going to parties? .Do things to relax at home or for leisure (reading, watching TV, sewing, listening to music)?” Possible answers for this question included “not at all difficult,” “a little difficult,” “only somewhat difficult,” “very difficult,” or “can’t do at all.” Social limitation is defined as a response of “somewhat difficult,” “very difficult,” or “cannot do at all” for any of the three questions. Other possible answers such as “do not do this activity,” “refused,” or “don’t know” were treated as missing data in the analysis. Work limitation Inability to work is operationalized in NHIS as either a respondent-defined limitation in the kind or amount of work that they can do or as a complete inability to work. Two questions are used to identify this status: “Does a physical, mental, or emotional problem NOW keep {you/ anyone in the family (age 18þ)} from working at a job or business?” If not yes: “{Are/any of these family members} limited in the kind OR amount of work {you/they} can do because of a physical, mental or emotional problem?” Answer categories include “yes,” “no,” “refused,” or “don’t know.” A positive answer on either question identified the person as having a work limitation. Basic actions difficulty Movement difficulty Movement actions without the use of assistive equipment are captured in terms of both upper body and lower body functions. The NHIS questions on movement difficulty are listed below and are prefaced with a reference to a health problem. “The next questions ask about difficulties you may have doing certain activities because of a HEALTH PROBLEM. By ‘health problem’ we mean any physical, mental, or emotional problem of illness (not including pregnancy).” “By yourself, and without using any special equipment, how difficult is it for you to .Walk a quarter of a miledabout 3 city blocks? .Walk up 10 steps without resting? .Stand or be on your feet for about 2 hours? .Sit for about 2 hours? .Stoop, bend, or kneel? .Reach up over your head? .Use your fingers to grasp or handle small objects? . . . Lift or carry something as heavy as 10 pounds such as a full bag of groceries?” Possible answers include “not at all difficult,” “only a little difficult,” “only somewhat difficult,” “very difficult,” or “can’t do at all.” Movement difficulty is defined as a response of “somewhat difficult,” “very difficult,” or “can’t do at all” on any of the questions. An answer of “only a little difficult” is treated as “not at all difficult,” and such a response is considered not disabled. Other possible answers such as “do not do this activity,” “refused,” or “don’t know,” were treated as missing data and not included in the analysis. A person is considered to have
B.M. Altman / Annals of Epidemiology 24 (2014) 2e7
movement difficulty if they responded that they had any difficulty with any of the movement questions. If a person had missing data on all eight questions about movement difficulty, they were not included in the charts or tables. Emotional difficulty Emotional difficulty is defined as having a score of 13 or more on the K6 serious psychological distress scale. The K6 instrument is a measure of psychological distress associated with unspecified but potentially diagnosable mental illness that may result in a higher risk for disability and a higher utilization of health services. In NHIS, the K6 is asked of adults 18 years of age and over. The K6 is designed to identify a person with serious psychological distress using as few questions as possible. The six items included in the K6 are as follows: “During the past 30 days, how often did you feel .So sad that nothing could cheer you up? .Nervous? .Restless or fidgety? .Hopeless? . . . That everything was an effort? .Worthless? Possible answers are “all of the time” (4 points), “most of the time” (3 points), “some of the time” (2 points), “a little of the time” (1 point), and “none of the time” (0 points). To score the K6, the points are added together yielding a possible total of 0 to 24 points. A threshold of 13 points or more is used to define serious psychological distress. Anyone answering some of the time to all six questions would not reach the threshold for serious psychological distress because, to achieve a score of 13, he or she would need to answer most of the time to at least one item.
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Sensory (seeing or hearing) difficulty Difficulties with seeing and hearing are based on two short sets of NHIS questions: “Do you have any trouble seeing, even when wearing glasses or contact lenses?” If the response is yes: “Are you blind or unable to see at all?” Respondents are counted as having a problem seeing if they indicate that they have trouble seeing even when wearing glasses or contact lenses or they report they are blind or are unable to see at all. The second set of questions is the following: “Have you ever worn a hearing aid?” “Which statement best describes your hearing without a hearing aid: Good, a little trouble, a lot of trouble, deaf?” Respondents are counted as having a problem hearing if they answer that they have a lot of trouble hearing without a hearing aid or that they are deaf. People who either currently use hearing aids or used them in the past, but do not report difficulty hearing, are not defined as having a problem. Cognitive difficulty The measure of cognitive function used here, although limited in breadth, captures at least some of the adults who are experiencing deterioration in memory or who exhibit signs of confusion. The measure is less likely to capture those with limited capacity for reasoning or decision making. The source of this question is the NHIS Family Core Questionnaire. {Are/Is} {person} LIMITED IN ANY WAY because of difficulty remembering or because {you/they} experience periods of confusion?” The answer categories are “yes,” “no,”“refused,” or “don’t know.” A positive answer identifies the respondent as having a cognitive difficulty.
Contents lists available at ScienceDirect
Annals of Epidemiology journal homepage: www.annalsofepidemiology.org
Disability symposium
Definitions, concepts, and measures of disability Barbara M. Altman PhD * Disability Statistics Consultant, Rockville, MD
a r t i c l e i n f o
a b s t r a c t
Article history: Received 24 September 2012 Accepted 3 May 2013 Available online 29 October 2013
The term “disability” is a shorthand expression or as explained in the International Classification of Functioning, Disability and Health an umbrella term. It has been used to identify the impairments that result from disease and injury, the physical, and mental or emotional functional limitations or difficulties a person has as a result of the impairments, as well as the participation restriction they experience when the environment is not supportive. Thus the term disability has been used to represent almost any of the conceptual components associated along the ability continuum that impacts the person, but it also includes the environmental effects that create a limiting impact from the context outside the person. This paper examines those concepts and definitions to provide insight into the measurement process to represent this important element of health and participation. Ó 2014 Elsevier Inc. All rights reserved.
Keywords: Disability Definitions Measurement Measurement purpose
Introduction On the basis of the current theoretical and legislative models of disability, there is general agreement that given the person’s level of physical, mental, or emotional functioning, the disablement process is associated with the nature of the interaction a person has with all aspects of his or her environment. That in turn can affect the level of social participation the person experiences. This paper briefly describes the conceptualization of the disability process as it proceeds from medical condition to restricted participation, and identifies the best way to measure the phenomenon for policy research use. Although disability can be attributed to the impairment or physical/mental outcome caused by a medical condition, it is also a social construct that results from the social and physical environment in which a person lives their life. Therefore, it is necessary to examine the complete process associated with the development of disability. The disability process, which may start with a disease, birth defect, or accident also includes the personal and environmental characteristics associated with the individual and although it contains numerous elements, the general nature of the process is fairly straightforward. The physical, mental, or emotional condition (disease or active pathology, injury, or congenital accident) that afflicts a person does (or does not) create an active physical, mental or emotional impairment in the cellular, organ, or limb levels of the individual in the active stage of the disease. When the acute phase * Corresponding author. Disability Statistics Consultant 14608 Melinda Lane Rockville, MD 20853. Tel: 301-460-5963. E-mail address: [email protected]. 1047-2797/$ e see front matter Ó 2014 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.annepidem.2013.05.018
of the disease, injury, or birth defect is completed, a residual impairment (abnormalities or losses that remain after the active disease pathology has been arrested or eliminated) can remain. The residual impairment also at the cellular, organ, or limb level can in some way change the capacity of those cells, that organ, or a limb so that they work differently than before the condition began. The residual impairment can create some physical, mental, or emotional functioning difficulties when the person attempts to act willfully. It can manifest as simply as creating a limp when walking across the room or with more complexity as when a person shuts down cognitively when in a stressful situation. These are examples of the possible functional limitations or difficulties a person brings to carrying on their life after disease, injury, or congenital accident. Whatever the functional limitation that is produced, it becomes a characteristic of the person, one of many. The impact of that functional limitation when the person interacts in their environment can be a risk factor for further limitation that is created by the receptivity or lack of receptivity of that environment to the specific type of functional limitation. Figure 1 provides a visual model of this process. The term “disability” has become a shorthand expression or an umbrella term that is used to represent the variety of the different aspects of the disability process [1]. It has been used to identify the active or residual impairments that result from disease and injury, as well as the physical, mental, or emotional functional limitations or difficulties a person has as a result of the residual impairments (as described), and also the participation restriction the person experiences when the environment is not supportive. So the term disability has been used to represent almost all of the conceptual components along the diseaseedisability continuum that impacts
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Fig. 1. Visual model of elements of disability process and their relationship [4].
the person, and it also is used to represent the results of the environmental effects that create a restriction or barrier outside of the person. As such, it has become a word almost without meaning, because it has been used to represent so many different aspects of the process. The term has been associated not only with different elements of the disability process, but also within the different time frames associated with the elements of the disability process. Additionally, it is used in a generalized way rather than with a specific orientation. So, for example, when used to represent functioning difficulties it indicates the point on the functional continuum at which the person exhibits a recognizable difference of reduced functional capacity/or performance from others or from the person’s own previous capacity or performance. However, this point is also linked to both the type of social roles in which a person participates and the physical and social environment in which they attempt to play those roles. Therefore the ‘disability’ may change or fluctuate based on the conceptual component focused on and the specifics of the individual’s characteristics (age, gender, race) and circumstances. When represented in measurement at the person level it may reflect general personal capacity but when represented in measurement by participation, it may also include numerous elements of participation role requirements and of the environmental context. From a social or policy perspective, we are concerned about identifying these environmental and personal elements so that we can provide social policy, education, or changes to improve the individual’s ability to enact their roles. Definition and measurement of disability then become important tools for improvement. However, a complicating factor in definition and measurement is that there is not a clearly marked separation between those with disabilities and those without disability. Although we try to treat disability as a dichotomous situationdeither a person is disabled or notdit is not the reality. People may be disabled in one situation and not another, depending on what is required of them, what the environmental conditions are, or what the purpose or objective of the definition used to describe the situation. Except for persons with very severe limitations who would be identified as disabled on any type of measurement scale, prevalence estimates of disability are subject to the basis of the measurement (what types of limitations, or activities are the point of focus) the person’s environmental situation at the point/time of measurement (is the weather, building structure, lighting or many other characteristics of the environment supportive or restrictive?) and the intent or purpose for which the estimate is required (are we attempting to ascertain the number of persons who will need fiscal support because they can’t work or are we identifying a group whose civil rights to access may be restricted or prevented?). This
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latter requirement is what forces us to create a dichotomy for policy purposes. However, the dichotomy is very different depending on the nature of the population defined by the analytic or policy purpose we are trying to measure. Examples of some of the many purposes for which we make disability prevalence estimates are numerous, but 2 very different general examples are most common. Civil rights purposes seek to impact on a broadly defined group, anyone with a disability; while benefit programs are organized for specific groups defined by their age, location or a specific characteristic or a specific condition or impairment. Different purposes use different definitions of disability, which highlight different conceptual elements and focus the measurement process on those highlighted elements. In large national surveys, it is much easier to identify and collect data on a generalized measure of functioning, such as mobility impairment, which can occur in a large number of condition and injury specific circumstances, than to collect information that accurately identifies specific diagnostic conditions so that the individual conditions are represented with a minimum of error. This means that national survey data are better suited to fulfilling a more generalized purpose, such as civil rights, than multiple more specific purposes linked with narrow programmatic definitions of the population to be served. Variety of Disability Definitions The Americans with Disabilities Act focuses on a civil rights purpose to promote the equalization of opportunities for all persons with disabilities. Based on the Equal Employment Opportunity Commission and the Department of Justice Americans with Disabilities Act Handbook, it includes both a focus on physical, mental, emotional functioning or some specific impairment that substantially limit functional actions, as well as related major life activities. It includes everything from breathing to participation in social life. A variety of enforcement areas are noted in the act, including equal employment opportunity and nondiscrimination in state and local government services, and the definition of disability which is encompassed is by far the broadest of all those found in federal legislation [2]. Social Security Disability Insurance represents a specific benefits program that provides income for workers whose disability is substantial enough to preclude employment. The definition includes a major focus on medical diagnosis (to substantiate the severity of the condition and associated limitation) and the demonstration of the inability to work. Thus, as with many other specific disability programs such as those directed at persons with intellectual and developmental disabilities, the definition of the qualifying population is more limited and, in the case of Social Security Disability Insurance, includes the types of conditions, the level of severity of the diagnoses, and the additional need to demonstrate an inability to work. A public health focus on disability is included in a wide range of legislation, but is not always separated as a unique category. It can either be inclusive of the broad population that experiences functional limitations in any area of action for concerns such as disparities in access to health care or evaluation of the overall costs to maintain health among this population, or it can be more narrowly focused on only those whose functional difficulties that create limitations in complex activities required to participate in the community. It can also focus on a subpopulation within the larger general population with disabilities either based on a specific type of functional limitation, such as mobility or cognitive limitations, a specific type of participation restriction such as difficulty maintaining self care independence, or, based on particular programmatic requirements, on a specific diagnosis such as autism or spinal cord
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injury. However, focus on a subgroup should not and cannot be generalized to the full population. Translating definition to measurement These three different orientations to purpose generate different specific aspects of the definitions which in turn highlight different components of the disablement process. Measurement, which tries to operationalize the specific conceptual element in a definition, will then come up with a variety of approaches to translating the specific conceptual element into real-world experiences and thus our estimates will vary and our measures may not even capture the same people. Each measure, which in a survey usually takes the form of a question or a series of questions, can only approximate a part of the population we seek, because a question can only generally tap one topic such as having difficulty walking or being unable to bathe or dress oneself. Definitions (legislative and other) are important for creating the focus, but measurement creates the data we use for analysis of all the questions we want to answer. Measurement of the various conceptual components can overlap, but cannot necessarily be used interchangeably. Measurement, not definition, provides our understanding of the outcomes of programs and identifies the service gaps. How do we find a real, everyday experience to represent the concepts we have chosen to identify as “disability”? If we focus on diagnosed medical conditions, we run into error because not everyone has a diagnosis or because the diagnosis can represent a wide range of disabling characteristics the individual may or may not exhibit. Take a diagnosis of diabetes. The person with diabetes may have several problems that create a disability, such as limited vision or an amputation. However, the person with a diabetes diagnosis can also have a well-controlled disease state without any physical, mental, or emotional limitations that influence their interaction in the environment. Should we really consider the latter person as disabled? If we choose to use a medical diagnosis as our indicator, we are at least separating those who have the potential to develop the functioning limitation or social participation restrictions associated with disability from those who for the moment have none. They may or may not experience residual impairment, and that can be followed by possible participation restriction. However, if we focus only on the actual physical, mental, or emotional limitations in functioning that results from residual impairments caused by the original disease state, we capture a more reasonable representation of the population that is at risk (with a greater potential) of participation restrictions depending on the environment in which they attempt that participation. The more elements of physical, mental, or emotional functioning we can include in the question sets the more likely we identify the majority of persons who will experience the disabling outcome that environments can create (one of the nice things about focusing on limitations in physical, mental, or emotional functioning is that we have a smaller potential group of items to include than the disease listings in the 9th edition of the International Classification of Diseases). Because the science has not yet identified valid and reliable measures of environments that limit participation, the closest we can come to identifying the population that has the potential to be limited in participation is to identify those with functional limitations that may or may not be accommodated environmentally. These are the persons we identify as being at risk, but whose outcomes are uncertain without the environmental component of the measurement, which should include not only the physical environmental barriers, but also those associated with attitudes of others. The person’s functional difficulties or limitations can put them at risk to experience disability, but it is the environmental (social and
physical) context that actually creates the level of participation restriction one experiences. There are two commonly used general measures in federal surveys todaydone that identifies the most commonly found functional difficulties or limitations and reflects the individual’s physical, mental and emotional functioning status as the whole person initiates willful activity. And twodbecause we cannot yet efficiently measure environment, we measure restricted participation which we assume results from some manner of environmental problems or barriers as the person performs their daily activities. These reflect the attempts at more complex activities, such as maintaining independence, working, and participating in social activities. The first form of measurement identifies, at the person level, limitations that, depending on environmental context, can be associated with participation limitation. The second form of measurement only identifies those who experience participation restrictions in their current settings and leaves out those who may experience participation restrictions in the event of transportation changes; movement to new, less supportive environments; or reductions in support funding. It is best not to identify disability based on health condition because not all people with health conditions experience functional limitation and not all people with functional limitations have necessarily been diagnosed with a medical condition. However, although we do not want to include fully functioning individuals in a measure of disability based just on a condition diagnosis, do we want to leave out of a count those with identified functioning issues who for the particular moment are able to participate in their present environment. In the latter case, the uncertainty factor is strong, especially in emergency type situations and in periods of financial uncertainty. For the most part, the measures discussed have been applied to adult populations. Measuring disability is a more complicated process among children, particularly young children, and those measures at this point in time focus on either special education attendance or medical diagnosis and have not evolved as the measures for adults have. Examples Using the National Health Interview Surveydone of the richest surveys in terms of disability measuresdthe next two figures provide examples of the two primary types of measurement sets and the possible uses of each [3]. The first type is located at the individual level and represents the person’s physical, mental, or emotional functioning capacity or performance. Figure 2 shows the measures in basic actions which represent these functioning difficulties. There are four components of the measures of basic actions: (1) Movement difficulty measures that capture the physical
Fig. 2. Percentage of adult population with functional difficulties in basic actions.
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Fig. 3. Percentages of adult population with participation limitations in complex activities.
limitations in moving arms, legs, fingers and body based on the level of difficulty the individual reports with walking, standing, sitting, grasping, etc.; (2) measures of sensory function including having difficulty or being unable to see or hear; (3) measures of cognitive functioning which focuses on remembering and concentrating; and (4) a measure of emotional functioning primarily based on level of feelings that could be associated with anxiety and/or depression based on the Kessler scale (more in-depth detail about the measures are provided in the Appendix). Functioning areas associated with communication, learning, and some areas of cognitive functioning are not yet well-represented by questions that have been developed and tested for survey use. These measures show that the four types of basic action measures taken altogether reveal that 29.5% of the adult population (approximately 62.3 million), ages 18 and over, indicate a difficulty in at least one area of physical, mental, or emotional functioning and can be considered at risk to develop a disability depending on the environment in which they act. The greatest proportion indicate a movement difficulty, 21.7%, whereas 13.1% report sensory functioning limitations, 3.1% report emotional difficulties, and 2.8% indicate cognitive functioning difficulties. Approximately 30.3% of the population with a basic action difficulty have difficulty with more than one area of functioning (more in depth detail about the data can be found by reviewing the reference at the website provided [3]). The second type of measure is related to activity located at the intersection of person with their environment and reflects their experience in that environment by indicating that either their participation/activities have been facilitated (they are involved in the activity) or restricted (they have some difficulty or cannot do the activity). In this instance, approximately 30.1 million persons indicate complex activity limitations associated with participation (Fig. 3). Participation restrictions can be caused by the severity of the person’s basic action difficulties, but it also can result from little to no accommodation, no assistive devices, or discriminatory actions in the environment; thus, not all disability reflected in a participation restriction measure is necessarily directly proportional to the individual’s difficulties or the severity of their health conditions. Approximately 14.3% of the adults 18 and over reported a limitation in some form of complex activity. The largest area of complex activity difficulty is the work area where 11.6% indicate they are limited or unable to work. Only 4.1% indicate difficulties with maintaining independence (based on activities of daily living or instrumental activities of daily living) and 6.9% have difficulties participating in leisure type activities [3]. As we commonly find, fewer than half of the persons who experience functional difficulties in basic actions in the National Health Information System (NHIS) data (Fig. 2) also indicate that they
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experience limitations in one or more of the measured complex activities (41.9% exactly) [3]. It should be noted that, although we have focused on two populationsdone with basic action difficulties and the second with complex activity limitationsdthese measures are a construct of several groups of questions representing various components of the disability process. In the first instance, basic action combines functional limitation characteristics of the individual and provides a person-level measure. In the second instance, the complex activity limitations combine to give us a representation of the person’s ability to participate within their environment. As indicated, the combination of the measures is what gives us our general prevalence estimates (either at the person level indicating risk of disability or at the participation level indication possible environmental restrictions). However, based on the research question, use of only one of those components of these general measures may be a reasonable use of the data. However, it should be kept in mind that movement difficulty does not represent the total population with basic action difficulty, nor does work limitation represent the total population with limitation in complex activities, only the largest component within that group. In addition, there is not complete overlap between persons with basic action difficulties and persons who report limitation in complex activities. About 3% of persons with complex activity limitations do not report any of the basic action difficulties measured in the NHIS data. The expectation is that they have difficulties with other basic actions that are not measured in the NHIS survey, such as learning difficulties, emotional problems not captured, or pain and fatigue that at the time of this data collection was not measured.
Conclusion Many who look at measurement today do not see any change or coming together of our approaches to measuring this population. But having studied the beginning of measurement in the US Census, starting with the two questions used in 1830 about being either deaf or blind, I do see movement toward a more coordinated approach. I would make several points to indicate the basis for that feeling. First, after 12 years of work, the international community, through the work of the Washington City Group, has come together on a set of six questions for use primarily in censuses. Approximately 30 counties used those questions in this recent round of censuses allowing for the very first time cross country comparisons based on the same questions. Those six questions reflect the most commonly occurring functional difficulties and some basic activities of daily living and instrumental activities of daily living. Second, the American Community Survey questions on disability that have successfully been implemented not only in the American Community Survey, but also in a variety of federal surveys, including the NHIS, the Current Population Survey, the Survey of Income and Program Participation, and the Crime Victimization Survey are very similar to what has been accepted by the international community. The American Community Survey questions, as a function of the role of census, provide a standard measure identifying this population for any number of program apportionments. Equally important the questions are providing our first standardization of disability measurement that has ever occurred across federal surveys and have been accepted as the basic measures to be used for the purposes of the new health care act. Finally, the future looks promising as well. Because the important intervention point to reduce or modify disability is with the environment, that is an area we must measure and address. There are several environmental measurement projects under way and it
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is just a matter of time before we have a reasonable set of questions to add to our surveys. The toughest problem is improving our measures of mental health functioning, incorporating more rare types of functioning limitations and adding areas such as pain and fatigue, which are important areas of difficulty for many individuals. Work in those areas are in the early stages.
References [1] World Health Organization. International classification of functioning, disability and health. Geneva, Switzerland: World Health Organization; 2001. [2] Americans with Disabilities Act of 1990 (ADA). P.L. 101-336 (July 26, 1990). Title 42 U.S.C. 12101 et seq. U.S. Statutes at Large, 104, 327e378. [3] Altman B,, Bernstein A. Disability and health in the United States, 2001-2005. Hyattsville, MD: National Center for Health Statistics; 2008. http://www.cdc. gov/nchs/data/misc/disability2001-2005.pdf. [4] Altman, B. Another perspective: capturing the working-age population with disabilities in survey measures, Journal of Disability Policy Studies http://dps. sagepub.com/content/early/2013/01/31/1044207312474309; February 4, 2013.
Appendix. Measurement of variables in Figures 1 and 21 Complex activity limitation Self-care limitation The self-care measure is based on National Health Information System (NHIS) questions on whether a person had difficulty with any component of either the activities of daily living (ADL) index or the instrumental activities of daily living (IADL) index, which are defined here: ADL are activities related to personal care and include bathing or showering, dressing, getting in or out of bed or a chair, using the toilet, and eating and getting around inside the home. In NHIS, respondents are asked whether they or family members 3 years of age and over need the help of another person with personal care because of a physical, mental, or emotional problem. People are considered to have an ADL limitation in NHIS if they respond affirmatively to the ADL questions and if the condition causing the respondent to need help with the specific activities is chronic (based on permanent chronic conditions such as diabetes or indications that the condition has existed for 3 months or more). IADL are activities related to independent living and include household chores, doing necessary business, shopping, or getting around for other purposes. In NHIS, respondents are asked whether they or family members 18 years of age and over need the help of another person for handling routine IADL needs because of a physical, mental, or emotional problem. People are considered to have an IADL limitation in NHIS if they respond affirmatively to the IADL questions and if the condition causing the respondent to need help is categorized as chronic (based on permanent chronic conditions such as diabetes or indications that the condition has existed for 3 months or more). Social limitation Social limitation is defined on the basis of three NHIS questions: “By yourself, and without using any special equipment, how difficult is it for you to .Go out to things like shopping, movies, or sporting events?
1 It should be noted that questions on pain and fatigue were added to the NHIS in 2011, after this material was originally presented.
.Participate in social activities such as visiting friends, attending clubs and meetings, going to parties? .Do things to relax at home or for leisure (reading, watching TV, sewing, listening to music)?” Possible answers for this question included “not at all difficult,” “a little difficult,” “only somewhat difficult,” “very difficult,” or “can’t do at all.” Social limitation is defined as a response of “somewhat difficult,” “very difficult,” or “cannot do at all” for any of the three questions. Other possible answers such as “do not do this activity,” “refused,” or “don’t know” were treated as missing data in the analysis. Work limitation Inability to work is operationalized in NHIS as either a respondent-defined limitation in the kind or amount of work that they can do or as a complete inability to work. Two questions are used to identify this status: “Does a physical, mental, or emotional problem NOW keep {you/ anyone in the family (age 18þ)} from working at a job or business?” If not yes: “{Are/any of these family members} limited in the kind OR amount of work {you/they} can do because of a physical, mental or emotional problem?” Answer categories include “yes,” “no,” “refused,” or “don’t know.” A positive answer on either question identified the person as having a work limitation. Basic actions difficulty Movement difficulty Movement actions without the use of assistive equipment are captured in terms of both upper body and lower body functions. The NHIS questions on movement difficulty are listed below and are prefaced with a reference to a health problem. “The next questions ask about difficulties you may have doing certain activities because of a HEALTH PROBLEM. By ‘health problem’ we mean any physical, mental, or emotional problem of illness (not including pregnancy).” “By yourself, and without using any special equipment, how difficult is it for you to .Walk a quarter of a miledabout 3 city blocks? .Walk up 10 steps without resting? .Stand or be on your feet for about 2 hours? .Sit for about 2 hours? .Stoop, bend, or kneel? .Reach up over your head? .Use your fingers to grasp or handle small objects? . . . Lift or carry something as heavy as 10 pounds such as a full bag of groceries?” Possible answers include “not at all difficult,” “only a little difficult,” “only somewhat difficult,” “very difficult,” or “can’t do at all.” Movement difficulty is defined as a response of “somewhat difficult,” “very difficult,” or “can’t do at all” on any of the questions. An answer of “only a little difficult” is treated as “not at all difficult,” and such a response is considered not disabled. Other possible answers such as “do not do this activity,” “refused,” or “don’t know,” were treated as missing data and not included in the analysis. A person is considered to have
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movement difficulty if they responded that they had any difficulty with any of the movement questions. If a person had missing data on all eight questions about movement difficulty, they were not included in the charts or tables. Emotional difficulty Emotional difficulty is defined as having a score of 13 or more on the K6 serious psychological distress scale. The K6 instrument is a measure of psychological distress associated with unspecified but potentially diagnosable mental illness that may result in a higher risk for disability and a higher utilization of health services. In NHIS, the K6 is asked of adults 18 years of age and over. The K6 is designed to identify a person with serious psychological distress using as few questions as possible. The six items included in the K6 are as follows: “During the past 30 days, how often did you feel .So sad that nothing could cheer you up? .Nervous? .Restless or fidgety? .Hopeless? . . . That everything was an effort? .Worthless? Possible answers are “all of the time” (4 points), “most of the time” (3 points), “some of the time” (2 points), “a little of the time” (1 point), and “none of the time” (0 points). To score the K6, the points are added together yielding a possible total of 0 to 24 points. A threshold of 13 points or more is used to define serious psychological distress. Anyone answering some of the time to all six questions would not reach the threshold for serious psychological distress because, to achieve a score of 13, he or she would need to answer most of the time to at least one item.
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Sensory (seeing or hearing) difficulty Difficulties with seeing and hearing are based on two short sets of NHIS questions: “Do you have any trouble seeing, even when wearing glasses or contact lenses?” If the response is yes: “Are you blind or unable to see at all?” Respondents are counted as having a problem seeing if they indicate that they have trouble seeing even when wearing glasses or contact lenses or they report they are blind or are unable to see at all. The second set of questions is the following: “Have you ever worn a hearing aid?” “Which statement best describes your hearing without a hearing aid: Good, a little trouble, a lot of trouble, deaf?” Respondents are counted as having a problem hearing if they answer that they have a lot of trouble hearing without a hearing aid or that they are deaf. People who either currently use hearing aids or used them in the past, but do not report difficulty hearing, are not defined as having a problem. Cognitive difficulty The measure of cognitive function used here, although limited in breadth, captures at least some of the adults who are experiencing deterioration in memory or who exhibit signs of confusion. The measure is less likely to capture those with limited capacity for reasoning or decision making. The source of this question is the NHIS Family Core Questionnaire. {Are/Is} {person} LIMITED IN ANY WAY because of difficulty remembering or because {you/they} experience periods of confusion?” The answer categories are “yes,” “no,”“refused,” or “don’t know.” A positive answer identifies the respondent as having a cognitive difficulty.
