2
Evolving Concepts of Disability

In 1955, when the Listing of Impairments was originally conceived and implemented, persons with disabilities were considered to be handicapped by their disease or impairment. Conceptually, disability was based on a medical model, in which disability is caused by a disease, injury, or other severe impairment for which the remedy, if any, is medical treatment. The Listings were accordingly based on body systems and severity of impairment. The nine examples of Listing-level impairments that the Social Security Administration (SSA) originally provided to guide decision making included the loss of vision, hearing, or speech; loss of use of two limbs; progressive diseases such as diabetes, multiple sclerosis, and heart and lung conditions that have resulted in major loss of physical function; terminal cancers; and neurological or mental impairments requiring institutionalization or constant supervision.1

Subsequently, the concept of disability has changed in recognition that disability, as distinct from impairment, is not just inherent in the individual and his or her medical condition but is the result of the interaction between the person with impairments and features of the socioeconomic environment in which the person lives, such as the presence or lack or acces-

1

These examples were first published by the director of the disability program in the Social Security Bulletin in 1957 (Hess, 1957:15). They were made part of SSA’s regulations in 1957 (22 FR 4362) and were the only examples of Listings until 1961, when additional conditions and factors were published, although without specific criteria for meeting the Listings (26 FR 5572).



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Improving the Social Security Disability Decision Process 2 Evolving Concepts of Disability In 1955, when the Listing of Impairments was originally conceived and implemented, persons with disabilities were considered to be handicapped by their disease or impairment. Conceptually, disability was based on a medical model, in which disability is caused by a disease, injury, or other severe impairment for which the remedy, if any, is medical treatment. The Listings were accordingly based on body systems and severity of impairment. The nine examples of Listing-level impairments that the Social Security Administration (SSA) originally provided to guide decision making included the loss of vision, hearing, or speech; loss of use of two limbs; progressive diseases such as diabetes, multiple sclerosis, and heart and lung conditions that have resulted in major loss of physical function; terminal cancers; and neurological or mental impairments requiring institutionalization or constant supervision.1 Subsequently, the concept of disability has changed in recognition that disability, as distinct from impairment, is not just inherent in the individual and his or her medical condition but is the result of the interaction between the person with impairments and features of the socioeconomic environment in which the person lives, such as the presence or lack or acces- 1 These examples were first published by the director of the disability program in the Social Security Bulletin in 1957 (Hess, 1957:15). They were made part of SSA’s regulations in 1957 (22 FR 4362) and were the only examples of Listings until 1961, when additional conditions and factors were published, although without specific criteria for meeting the Listings (26 FR 5572).

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Improving the Social Security Disability Decision Process sible transportation and practical workplace accommodations. Under this concept, two people with the same impairment might have quite different degrees of work disability. For example, a person with an injury that permanently limits use of an arm, who is 55 years old, has limited education, and has a work history of manual labor, would be very disabled, while a person with the same impairment with a law degree may not be disabled at all. Similarly, two people with impairments of quite different severity might be equally disabled from working. Several commonly used models of disability exist today, but all distinguish in some way between impairment, functional capacity, and disability (IOM, 1991; Nagi, 1976; WHO, 1980). More recent conceptualizations of these models have added external barriers to participation as factors in disability (IOM, 1997; NCMRR, 1993; WHO, 2001). These conceptual models were developed largely to help rehabilitation researchers understand the factors that disable people and to develop and evaluate interventions that reduce disability. They have also been stimulated by and useful in dealing with environmental barriers whose elimination would reduce the disability of impaired persons. Although these disability models were not developed for SSA’s disability programs, which provide cash assistance to individuals whose impairments prevent them from engaging more than minimally in gainful activity, it is useful to distinguish among impairment, function, and disability when analyzing the basis for the Listings. Some of these models of disability are described next in this chapter, followed by a discussion of how the SSA process for determining disability matches with current concepts of factors contributing to disability, especially the role of the Listings criteria in the process. CONCEPTUAL MODELS OF DISABILITY This section presents the conceptual evolution of disability in terms of a series of models that have been proposed since the advent of the Social Security Disability Insurance (SSDI) program. They are: Nagi’s Disability Model World Health Organization’s (WHO’s) International Classification of Impairment, Disability, and Handicap (ICIDH) National Center for Medical Rehabilitation Research (NCMRR) Model Verbrugge and Jette’s Model of the Disablement Process Institute of Medicine’s (IOM’s) Enabling-Disabling Model WHO’s International Classification of Functioning, Disability and Health (ICF)

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Improving the Social Security Disability Decision Process Nagi’s Disability Model In the 1960s and 1970s, Saad Z. Nagi developed an influential model of disability based on his research on rehabilitation outcomes (Nagi, 1964, 1965, 1976, 1987). Nagi differentiated among concepts of pathology, impairment, functional limitations, and disability, making them separate components of his model (Table 2-1). By using the term “disability” instead of “handicap,” he avoided giving the concept a negative connotation; that is, he did not suggest an absolute limitation, one that failed to take into account circumstances outside the control of the person with a given health condition. Nagi considered disability to result from the interaction of a person with a health condition with his or her environment, which includes family support, employer accommodations, and physical and sociocultural barriers. Nagi also acknowledged other factors affecting disability, including the person’s own characteristics and definition of the situation. He noted that not all impairments or functional limitations result in disability; two individuals with similar pathologies, impairments, and functional ca- TABLE 2-1 Comparison of Components of Models of Disablement Model Components of the Model Cells/Tissue Organ Person Society External Barriers Nagi, 1969 Pathology Impairment Functional limitation Disability   IOM Modification of Nagi Model, 1991 Pathology Impairment Functional limitation Disability Social and physical environment ICIDH (WHO, 1980) Disease Impairment Disability Handicap   NCMRR, 1993 Pathophysiology Impairment Functional limitation Disability   Vergrugge-Jette, 1994 Pathology Impairments Functional limitations Disability   IOM, 1997 Pathology Impairment Functional limitation Disabililty   ICF (WHO, 2001) Body functions and structures Activity Participation Personal and environmental factors SOURCE: Adapted in part from Butler et al., 1999.

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Improving the Social Security Disability Decision Process pacities might have different patterns of disability, while similar patterns of disability might result from different kinds of health conditions. Nagi provided an update of his model as an appendix to the 1991 report of the IOM, Disability in America. In it, he noted that certain disfiguring or stigmatizing impairments could result in disability without causing functional limitations at the organism level (Nagi, 1991:315). The IOM report added several dimensions to the Nagi model. First, it proposed three interacting risk factors—biological, environmental (social and physical), and lifestyle/behavioral—that affect each element of the disabling process: pathology, impairment, functional limitation, and disability. Second, it added impact on quality of life as a part of the disabling process (IOM, 1991:84-91). In effect, it added another component to Nagi’s model—features of the social and physical setting affecting an individual’s degree of disability that could be targeted for change (Table 2-1). The IOM report helped bring Nagi’s conceptual model of disability to a wider audience and helped stimulate research on the environmental aspects of the disablement process. Nagi’s concepts strongly influenced other models of disability, including those of the WHO and the NCMRR (both described below) and were adopted by rehabilitation organizations, such as the American Physical Therapy Association. WHO’s International Classification of Impairment, Disability, and Handicap (ICIDH) WHO developed the ICIDH to complement the International Classification of Diseases (ICD) (WHO, 1980). The ICD classifies diseases, disorders, and other health conditions by diagnosis and is used to identify acute illnesses and injuries that can be cured or prevented. The ICD is not, however, well suited to classifying and tracking chronic or progressive disorders (Whiteneck, 2006:51). Therefore, WHO developed the ICIDH to classify the kinds and levels of function and disability associated with health conditions (Jette, 2006:730). The ICIDH made conceptual distinctions, based on Nagi, among impairment, functional limitations (which, however, WHO called “disability”), and disability (called “handicap” by WHO), which allowed recognition that disability is based not just on the attributes of the individual (the medical model) but also on the interaction between the person and society (the biopsychosocial model) (Table 2-1). On the negative side, the ICIDH used the word “handicap” to label the result of the interaction between the person and the social setting. This label seemed to perpetuate the idea that the problem is more the inability of the person to fit into usual social roles rather than restrictions imposed by environmental barriers and social atti-

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Improving the Social Security Disability Decision Process tudes, which could be modified to enable an impaired person to participate in work and other normal activities. The model was also still medically based (i.e., diseases, injuries, or other disorders result in impairment, which cause functional limitations, which, in turn, reduce the person’s ability to participate in society). This did not recognize the complexity of the disablement process, especially the role of contextual factors, or the fact that the correlations between degree of impairment, extent of functional limitation, and level of disability are low. National Center for Medical Rehabilitation Research Model NCMRR (1993) built on the Nagi model by including the impairment, functional limitation, and disability domains corresponding to the organ, person, and societal levels, but NCMRR added another level or “dimension,” called “societal limitation” (Table 2-1). In the NCMRR model, societal limitations are barriers to full participation in society that result from attitudes, architectural barriers, and social policies. The NCMRR model pulled external barriers out of the environmental domain for special emphasis, highlighting the fact that these barriers could be reduced or eliminated by public policy. Verbrugge and Jette’s Model of the Disablement Process Verbrugge and Jette elaborated on Nagi’s model in “an attempt to attain a full sociomedical framework of disablement, which they defined as the impact that chronic and acute conditions have on functioning of specific body systems and on people’s abilities to act in necessary, usual, expected, and personally desired ways in their society” (Jette, 2006:729). Altman (2001) notes that Verbrugge and Jette focused on task orientation, while Nagi focused more on role orientation toward limitation. As already noted, Verbrugge and Jette accepted the elements of Nagi’s model: active pathology, impairment, functional limitation, and disability (Table 2-1). They operationalized the Nagi model by identifying various types of necessary, usual, expected, and/or personally desired roles and activities under Nagi’s concept of disability that should be tracked and measured. These included (Verbrugge and Jette, 1994): Basic activities of daily living—including behaviors such as basic personal care Instrumental activities of daily living—including activities such as preparing meals, doing housework, managing finances, using the telephone, and shopping

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Improving the Social Security Disability Decision Process Paid and unpaid role activities—including occupation, parenting, grandparenting, and student roles Social activities—including attending church and other group activities, and socializing with friends and relatives Leisure activities—including sport and physical recreation, reading, distinct trips, and so on In addition Verbrugge and Jette (1994) tried to make the model more dynamic by identifying factors that affect what they called the “disablement process.” They posited three sets of variables that affected the “pathway” to disablement of a given individual. These were: Risk Factors. Risk factors are “predisposing phenomena that are present prior to the onset of the disabling event that can affect the presence or severity of the disablement process. Examples include sociodemographic background, lifestyle, and biologic factors.” Intra-individual Factors. Intra-individual factors “operate within a person, such as lifestyle and behavioral changes, psychosocial attributes and coping skills, and activity accommodations made by the individual following onset of a disabling condition.” Extra-individual Factors. Extra-individual factors are in the external “physical as well as the social context in which the disablement process occurs. Environmental factors relate to the social as well as the physical environmental factors that bear on the disablement process. These can include medical and rehabilitation services, medications and other therapeutic regimens (e.g., exercise or physical activity), external supports available in the person’s social network, and the physical environment.” Verbrugge and Jette stimulated research into the impact of risk factors, intra-individual factors, and extra-individual factors on impairment, functional limitation, and disability and how they influence the disablement process. Jette (2006) cites a number of examples of this research: Lawrence and Jette (1996), Jette et al. (1998), Guralnik et al. (1994, 1995), Gill et al. (1995), and Ostir et al. (1998). IOM’s Enabling-Disabling Model (1997) In 1997, an IOM committee issued a report, Enabling America: Assessing the Role of Rehabilitation Science and Engineering, which responded to a congressional request for an assessment of rehabilitation research and technology development efforts. The report extended the 1991 IOM model by making “clear reference to the importance of the environment in causing, preventing, and reducing disability” (IOM, 1997:1).

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Improving the Social Security Disability Decision Process The committee explicitly adopted the elements of Nagi’s disability model (but called them “components of the disabling process” in the report)—i.e., pathology, impairment, functional limitation, and disability—with disability defined as “a limitation in performing certain roles and tasks that society expects of an individual” (Table 2-1). The IOM report focused on the “enabling process,” by which it meant efforts to reduce disability. Enabling could be accomplished by either restoring function in the individual (i.e., traditional rehabilitation) or expanding access to the environment, or both. The report also introduced the notion of secondary conditions as “any additional physical or mental health condition that occurs as a result of having a primary disabling condition” and that “quite often increase the severity of an individual’s disability and are also highly preventable” (IOM, 1997:3-5). According to the report, “the committee enhanced the 1991 IOM model to show more clearly how biological, environmental (physical and social), and lifestyle/behavioral factors are involved in reversing the disabling process, i.e., rehabilitation, or the enabling process. The enhancements include bidirectional arrows between the various states of the enabling–disabling process to indicate that the disabling process (described in the 1991 IOM model) can be reversed with proper interventions (i.e., the enabling process)” (IOM, 1997:6). The graphic representation of the new IOM model did not include a box for “disability,” in an effort “to help clarify the fact that disability is not inherent in the individual, but rather is a product of the interaction of the individual with the environment” (IOM, 1997:8). The report proceeded to recommend research and engineering needs and opportunities by domain: pathology and impairment research, functional limitation research, and disability research. Disability research would be “explicitly focused on the effects of the environment in producing or reducing disability” (IOM, 1997:12). In the report, the committee noted that the 1991 IOM model had some shortcomings. First, disability was depicted in the 1991 model as a linear process, which was fine for the 1991 report’s focus on ways to prevent disability but did not allow for reversal of disability through rehabilitation. Second, the earlier model gave a “limited characterization of the environment and the interaction of the individual with the environment.” Third, the 1991 model provided a limited “representation of societal limitations” (IOM, 1997:67). WHO’s International Classification of Functioning, Disability and Health (ICF) ICF resulted from a substantial revision of the 1980 ICIDH. ICF is based on the premise, supported by studies, that diagnosis alone does not predict service needs, length of hospitalization, level of care, or functional

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Improving the Social Security Disability Decision Process outcomes (WHO, 2001). In addition, the presence of a disease or disorder is not an accurate predictor of receipt of disability benefits, work performance, return-to-work potential, or likelihood of social interaction. In the ICF, disability and functioning are seen as outcomes of interactions between health conditions and contextual factors. Contextual factors include external environmental factors, such as social attitudes, architectural characteristics, and the legal system, and internal personal factors, such as sex, age, coping styles, social background, education, profession, and other factors that influence how disability is experienced by an individual (WHO, 2001:214). ICF is a rather complicated classification system, because its elements are interactive. Its domains include (Table 2-1): Impairments in Body Functions and Structures “Body functions are the physiological functions of body systems (including psychological functions).” “Body structures are anatomical parts of the body such as organs, limbs and their components.” “Impairments are problems in body function or structure such as a significant deviation or loss.” Limitations on Activities and Limitations on Participation “Activity is the execution of a task or action by an individual.” “Participation is involvement in a life situation.” “Activity limitations are difficulties an individual may have in executing activities.” “Participation restrictions are problems an individual may experience in involvement in life situations.” Environmental Factors. “Environmental factors make up the physical, social and attitudinal environment in which people live and conduct their lives.” Although the ICF model is comprehensive, it is complex and difficult to operationalize. This and other shortcomings of the ICF are discussed in Whiteneck (2006). The main problem is distinguishing between activity limitations and participation limitations, which have shared activities in the model. SUMMARY During the past 50 years, researchers in rehabilitation have developed conceptual models of disability that have evolved in accord with a general

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Improving the Social Security Disability Decision Process consensus that it is useful to distinguish impairments, functional limitations, and disabilities, and to conceive of disability as an outcome of the interaction between specific individuals with health conditions and the environments in which they find themselves. Work disability, for example, results from the interaction of individuals’ impairments, functional limitations resulting from the impairments, assistive technologies to which they may have access, and attitudinal and other personal characteristics (such as age, education, skills, and work history) with the physical and mental requirements of potential jobs, accessibility of transportation, attitudes of family members and coworkers, and willingness of an employer to make accommodations. CONCEPTUAL BASIS OF THE LISTINGS Disability in the SSDI and Supplemental Security Income (SSI) programs is legally defined as a “medically determinable physical or mental impairment” that prevents an individual from engaging in “substantial gainful activity” and is expected to last (or has lasted) at least 12 months or to result in death. Because children are not expected to engage in substantial gainful activity, childhood disability under SSI is defined as a physical or mental condition or combination of conditions that causes “marked and severe functional limitations” and is expected to last (or has lasted) at least 12 months or to result in death. It has elements of the medical model, because from the beginning, Congress has wanted to limit the program by requiring that the reason for work limitations be identified as medical (Stone, 1984). SSA thus requires a medical diagnosis and medical evidence (e.g., tests or examinations) that supports or is consistent with the claimant’s work disability (or with marked and severe functional limitations if a child). In terms of contemporary concepts of disability, the Social Security definition corresponds to a participation restriction, namely, severe or complete difficulty in engaging in remunerative employment. Applicants for Social Security benefits who do not meet or equal the Listings are given a residual functional capacity (RFC) evaluation, based on information provided by treating sources, other medical sources (e.g., nurse-practitioners, physicians’ assistants, audiologists, and physical and occupational therapists), and nonmedical sources (e.g., teachers, counselors, social workers, spouses, parents, friends, neighbors, and clergy). The RFC includes both activity limitations, such as activities of daily living, and participation restrictions, such as work history. It takes into account nonmedical factors, such as age, education, training, and work experience, and also variable access to health care and assistive technology that, if available, might reduce disability. It cannot, however, take into account all the factors in disability, for example,

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Improving the Social Security Disability Decision Process accessibility to potential work sites or willingness of employers to make accommodations. But determining whether someone meets the SSA disability standard by taking all these factors into account is complex and time consuming. Accordingly, SSA developed the Listings as a screening tool to identify obviously disabled applicants without having to go through the full evaluation process. The criteria in the Listings, however, are generally not measures of disability. Listings criteria are mostly measures of the severity of impairment and degree of functional limitations on organs or body systems (e.g., treadmill tests, pulmonary function test, range of motion of joints, and IQ tests). Conceptually, most criteria in the Listings are based on evaluation of body functions and structures, and some are based on activity limitations, such as activities of daily living. The criteria are based on the assumption that, for the conditions in the Listings, there is a strong correlation between the presence of a severe impairment or functional limitation and inability to work. For example, a person is considered disabled by SSA if they are not working and have chronic diminished pulmonary function, documented by having specified values on a one-second forced expiratory volume or forced vital capacity test (Listing 3.02). Applicants with heart conditions meet the Listings and receive benefits if they have a left ventricular ejection fraction of 30 percent or less and are unable to perform on an exercise test at a workload equivalent of 5 metabolic equivalents of task or less without exhibiting certain signs or symptoms, such as electrocardiogram abnormalities or chest pain (Listing 4.02). Some listings are based on a diagnosis alone, such as amyotrophic lateral sclerosis (Listing 11.00) and malignancies that are inoperable or unresectable or that are progressive and unresponsive to treatment (e.g., Listing 13.09, metastatic melanoma). The mental and childhood listings, however, include results of testing, where they are appropriate (e.g., IQ tests in the mental retardation listing), but they also consider factors in the disability domain, such as social and employment limitations.2 Some of the Listings have an evidence basis and others are based on expert consensus. The report addresses the importance of research on the relationships among impairment, functional capacity, and work disability as a basis for evidence-based Listings in Chapter 7. Meanwhile, it is important to keep in mind that the Listings essentially correspond to the impairment and to some degree what is called activity limitations domains and, with some exceptions, do not consider factors in the disability domain. The concept is that the listings in the Listings of Impairments constitute a screening 2 An IQ of 59 or less alone meets a listing (Listing 12.05B for adults or Listing 11.205C for children).

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Improving the Social Security Disability Decision Process test based on severity criteria that are so high that claimants who meet or equal them can be presumed unable to work. In other words, judged by the gold standard of SSA disability, the Listings are expected to have high specificity (that is, a low false-positive rate). Of course, an imperfect test required to have high specificity will, by nature, have limited sensitivity (e.g., it will miss identifying true positives). The only way to avoid such inherent tradeoffs is to improve the test, that is, enhance its ability to separate SSA-disabled from SSA-non-disabled claimants, or choose a better test. REFERENCES Altman, B.M. 2001. Disability definitions, models, classification schemes, and applications. In Handbook of disability studies, edited by G. Albrecht, K.D. Seelman, and M. Bury. Thousand Oaks, CA: Sage Publications. Pp. 97-122. Butler, C., H. Chambers, M. Goldstein, S. Harris, J. Leach, S. Campbell, R. Adams, and J. Darrahet. 1999. Making sense of research in developmental disabilities: A conceptual framework for reviewing treatment outcomes. Developmental Medicine and Child Neurology, 41(1):55-59. Gill, T.M., C.S. Williams, and M.E. Tinetti. 1995. Assessing risk for the onset of functional dependence among older adults: The role of physical performance. Journal of the American Geriatric Society, 43:603-609. Guralnik, J.M., E.M. Simonsick, L. Ferrucci, et al. 1994. A short physical performance battery assessing lower extremity function: Association with self-reported disability and prediction of mortality and nursing home admission. Journal of Gerontology, 49:M85-M94. Guralnik, J.M., L. Ferruci, E.M. Simonsick, et al. 1995. Lower-extremity function in persons over the age of 70 years as a predictor of subsequent disability. New England Journal of Medicine, 232:556-561. Hess, A.E. 1957. Old-age, survivors, and disability insurance: Early problems and operations of the disability provisions. Social Security Bulletin, 12:11-21. IOM (Institute of Medicine). 1991. Disability in America: Toward a national agenda for prevention, edited by A.M. Pope and A.R. Tarlov. Washington, DC: National Academy Press. IOM. 1997. Enabling America: Assessing the role of rehabilitation science and engineering. Edited by E. Brandt and A.M. Pope. Washington, DC: National Academy Press. Jette, A.M. 2006. Toward a common language for function, disability, and health. Physical Therapy, 86(5):726-734. Jette, A.M., S.F. Assmann, D. Rooks, B.A. Harris, and S. Crawford. 1998. Interrelationships among disablement concepts. The Journals of Gerontology Series A: Biological Sciences and Medical Sciences, 53A:M395-M404. Lawrence, R.H., and A.M. Jette. 1996. Disentangling the disablement process. The Journals of Gerontology Series B: Psychological Sciences and Social Sciences, 51:S173-S182. Nagi, S. 1964. A study in the evaluation of disability and rehabilitation potential: Concepts, methods, and procedures. American Journal of Public Health, 54:1568-1579. Nagi, S. 1965. Some conceptual issues in disability and rehabilitation. In Sociology and rehabilitation, edited by M.B. Sussman. Washington, DC: American Sociological Association. Pp. 100-113. Nagi, S.Z. 1969. Disability and rehabilitation: Legal, clinical, and self-concepts and measurements. Columbus: Ohio State University Press.

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Improving the Social Security Disability Decision Process Nagi, S.Z. 1976. An epidemiology of disability among adults in the United States. Milbank Memorial Fund Quarterly, 54:439-467. Nagi, S.Z. 1987. The concept and measurement of disability. In Disabled Policies and Government Programs, edited by E.D. Berkowitz. New York: Praeger. Nagi, S.Z. 1991. Disability concepts revised: Implication for prevention. In Disability in America: Toward a national agenda for prevention, edited by A.M. Pope and A.R. Tarlov. Washington, DC: National Academy Press. Pp. 309-327. NCMRR (National Center for Medical Rehabilitation Research). 1993. Research plan for the National Center for Medical Rehabilitation Research, National Institute of Child and Human Development, NIH, DHHS. Washington, DC: U.S. Government Printing Office. Ostir, G.V., K.S. Markides, S.A. Black, and J.S. Goodwin. 1998. Lower body functioning as a predictor of subsequent disability among older Mexican Americans. The Journals of Gerontology Series A: Biological Sciences and Medical Sciences, 53:M491-M495. Stone, D.A. 1984. The disabled state. Philadelphia, PA: Temple University Press. Verbrugge, L.M., and A.M. Jette. 1994. The disablement process. Social Science & Medicine, 38(1):1-14. Whiteneck, G. 2006. Conceptual models of disability: Past, present, and future. In Workshop on disability in America: A new look, edited by M. Field, A.M. Jette, and L. Martin. Washington, DC: The National Academies Press. Pp. 50-66. WHO (World Health Organization). 1980. International classification of impairments, disabilities, and handicaps. Geneva: WHO. WHO. 2001. International classification of functioning, disability and health: ICF. Geneva: WHO.