2
Magnitude and Dimensions of Disability in the United States

Disability is a serious public health and social issue in the United States. About 35 million Americans experience activity limitations owing to chronic health problems or impairments, and many of them are deprived economically and socially because of these limitations. They incur high health care costs and have special problems in accessing health care. Despite the apparent magnitude of the problem, however, few comprehensive assessments of the prevalence and nature of disability in the United States are available (Rice and LaPlante, 1988a).

Data on disability come from a wide variety of data systems, each of which collects data for its own purposes, requiring different standards and definitions. These different purposes provide for a rich diversity of information on disability in the United States, but the resulting differences in definitions and statistical practices make it difficult to assess the full public health and social impacts of disability in a comprehensive way (National Research Council, 1990).

This chapter reviews data from several of these systems. Comparing and synthesizing those data, it presents an analysis of the dimensions of disability in the United States, now and in the past, and describes the prevalence of disability and its associated chronic health conditions in the population. The focus is on the broad dimensions of disability rather than on special problems or populations. Similarly, this analysis focuses on the prevalence of disabling conditions, not on the causes of these limitations. This is followed by a brief discussion of the economic costs of disability.

DATA SOURCES

Students of disability-related issues continue to debate the best statistical system for assessing and analyzing the dimensions of disability (National



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Disability in America: Toward a National Agenda for Prevention 2 Magnitude and Dimensions of Disability in the United States Disability is a serious public health and social issue in the United States. About 35 million Americans experience activity limitations owing to chronic health problems or impairments, and many of them are deprived economically and socially because of these limitations. They incur high health care costs and have special problems in accessing health care. Despite the apparent magnitude of the problem, however, few comprehensive assessments of the prevalence and nature of disability in the United States are available (Rice and LaPlante, 1988a). Data on disability come from a wide variety of data systems, each of which collects data for its own purposes, requiring different standards and definitions. These different purposes provide for a rich diversity of information on disability in the United States, but the resulting differences in definitions and statistical practices make it difficult to assess the full public health and social impacts of disability in a comprehensive way (National Research Council, 1990). This chapter reviews data from several of these systems. Comparing and synthesizing those data, it presents an analysis of the dimensions of disability in the United States, now and in the past, and describes the prevalence of disability and its associated chronic health conditions in the population. The focus is on the broad dimensions of disability rather than on special problems or populations. Similarly, this analysis focuses on the prevalence of disabling conditions, not on the causes of these limitations. This is followed by a brief discussion of the economic costs of disability. DATA SOURCES Students of disability-related issues continue to debate the best statistical system for assessing and analyzing the dimensions of disability (National

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Disability in America: Toward a National Agenda for Prevention Research Council, 1990). As defined and described throughout this report, much of "disability" is a social issue, going beyond biological or functional limitations and relating to people's ability to perform their expected social roles. This chapter, however, attempts to avoid the debate about how disability should be defined and measured, and simply reports on the data that are available. The National Health Interview Survey (NHIS) is a population survey that has been conducted continuously by the National Center for Health Statistics for almost 30 years (National Center for Health Statistics, 1989a). The NHIS data, particularly the data on "activity limitation," provide a reasonably consistent national picture over a long period of time, and hence are used as the framework of the synthesis in this chapter. These data are supplemented, where appropriate, by data from other surveys described below. The National Health Interview Survey (NHIS) The NHIS is designed to collect representative data on the civilian noninstitutionalized population living in the United States. Among those excluded from the scope of the NHIS are residents of nursing homes, members of the armed forces, prisoners, and U.S. citizens living abroad. In 1988, the survey reached a sample of 122,310 persons in 47,485 households. The use of households to locate survey respondents means that the NHIS tends to underrepresent that portion of the population, the homeless, for example, that do not live in households. To the extent possible, adults are interviewed directly. Proxy respondents provide information for all children in the household and for those adults who cannot be interviewed in person (National Center for Health Statistics, 1989a). The NHIS data on activity limitation are obtained through questions that establish whether an "impairment or health problem" prevents or limits activities and whether that impairment or health problem is chronic. Respondents are further classified according to the degree of activity limitation: (1) limited, but not in "major activity" (the least severely limited category); (2) limited in amount or kind of "major activity"; or (3) unable to carry out "major activity'' (the most severely limited category). "Major activity" is defined as the predominant social role expected of a person of a given age. According to the current definition, the major activities are "playing" for children under age 5, "attending school" for children ages 5-17, "working or keeping house" for adults ages 18-69, and "living independently" for adults age 70 and over. As discussed below in the section on trends, however, these definitions have changed over time (National Center for Health Statistics, 1989a). A chronic condition is one that has existed for at least three months or

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Disability in America: Toward a National Agenda for Prevention one such as arthritis or heart disease that would normally continue for at least three months. Respondents who have more than one limiting condition are asked to identify one of them as the main cause of their limitation. Identification of these causes depends on the respondents' understanding of their conditions, their perceptions of how limiting they are, and their willingness to report them. In a separate set of questions, the NHIS also collects data on the overall prevalence of specific chronic conditions, without regard to whether the condition causes any activity limitation (National Center for Health Statistics, 1989a). This distinction between presence of a condition and limitation caused by a condition is consistent with the distinction that has been made between impairments or functional limitations and disability (Nagi, 1965; World Health Organization, 1980; Haber, 1990). The ICD Survey of Disabled Americans In late 1985, Louis Harris and Associates conducted a telephone survey for the International Center for the Disabled (ICD) and the National Council on the Handicapped to assess the attitudes and experiences of people with disabilities. The survey was designed to reach a representative sample of the population age 16 and over with disabilities, living in households with telephones in all states except Alaska and Hawaii. Individuals were included if they met any one of three criteria: (1) having a health condition that prevented full participation in work, school, or other activities; (2) having a physical disability, a seeing, hearing, or speaking impairment, an emotional or mental disability, or a learning disorder; or (3) reporting that one considered oneself disabled or that others would consider one disabled. In addition to questions on the nature and severity of their disability, the survey asked respondents about the impact of disability on their social and working lives, barriers to entering the mainstream, disability benefits, and other matters. The survey's methodology permitted an estimate of the prevalence of disability in the United States (Louis Harris and Associates, 1986). Survey of Income and Program Participation (SIPP) Conducted by the Census Bureau since 1983, the SIPP is an ongoing panel study of the economic well-being of U.S. households. In 1984, during the third round of interviews with its first panel, SIPP collected data on the extent of disability in the civilian noninstitutionalized population. These data include information on: (1) functional limitations; (2) work limitations; and (3) receipt of Social Security or veterans disability benefits (U.S. Department of Health and Human Services, 1989d).

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Disability in America: Toward a National Agenda for Prevention For adults, the degree of functional limitation was based on ability to perform activities of daily living (ADLs),1 three of the standard instrumental activities of daily living (IADLs)2 (Katz, 1983), and six other sensory and physical functions. Individuals needing assistance with ADLs were the most severely limited, followed by those needing assistance with IADLs. A broader category of limitation—a "substantial" limitation—included all of those needing assistance with ADLs or IADLs plus people who were unable to perform one or more of the sensory or physical functions, or who had difficulty with two or more of those functions. For children, functional limitation was based on the presence of either a physical condition that limits the ability to walk, run, or play, or a mental or emotional condition that limits the ability to learn or do school work. These limitations in children were considered equivalent to "substantial" limitations in adults. Questions on work limitations were asked of persons ages 16-72. Unlike the NHIS, limitations due to acute conditions were not excluded. The data on receipt of disability benefits cover the noninstitutional resident population ages 18-64. National Long-Term Care Surveys (NLTCS) In 1982 and again in 1984, the Health Care Financing Administration conducted surveys of the Medicare-eligible population aged 65 and over to assess the characteristics of persons with chronic disabilities. Both surveys defined disability as a current or expected limitation of 90 days or more in the ability to perform one or more ADLs or IADLs. For the 1982 survey, interviews were conducted only with people living in the community; residents of nursing homes were excluded (Manton, 1989; Macken, 1986). The 1984 survey reinterviewed survivors from the first study, including those who had moved into nursing homes, and conducted first-time interviews with new respondents (Manton, 1989). Supplement on Aging (SOA) and Longitudinal Study of Aging (LSOA) Each year the NHIS supplements its core questionnaire with additional questions on special topics. In 1984 the special topic portion of the NHIS, the Supplement on Aging (SOA), addressed the health status and living arrangements of people aged 55 and older. The SOA collected detailed data on subjects that included the respondents' ability to perform ADLs and 1   Dressing, undressing, eating, personal hygiene, getting in/out of bed, and getting around inside the house. 2   Preparing own meals, doing light housework, and getting around outside the house.

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Disability in America: Toward a National Agenda for Prevention IADLs, the presence of specific health impairments, and the respondents' work histories and disability benefits. The SOA also served as the baseline of a longitudinal study, the Longitudinal Study of Aging (LSOA), intended to study the impact of changes in functional status and living arrangements on institutionalization. The LSOA used three forms of follow-up: the National Death Index was used to locate those SOA respondents who died; Medicare files were used to determine hospital use and costs for respondents who were 65 or older at the time of the SOA interview; and surviving respondents who were 70 or older at the time of the SOA were reinterviewed in 1986 and 1988 (National Center for Health Statistics, 1987b). PREVALENCE OF DISABILITY Based on the 1988 NHIS, 33.1 million people, or 13.7 percent of the civilian noninstitutionalized population, have some degree of "activity limitation" due to chronic conditions. When one takes into account the estimated 2.2 million people with disabilities who live in institutional facilities such as nursing homes or residential facilities for the mentally retarded or mentally ill (U.S. Department of Health and Human Services, 1989d), the total number of Americans with disabilities is about 35 million. To describe the composition of this population, we begin with data on activity limitation from the NHIS and then use data from other sources to provide different perspectives. NHIS Activity Limitation Data The 33.1 million noninstitutionalized people with activity limitations fall into three groups of roughly equal size. Some 10.3 million (4.3 percent of the population) experience limitations that do not interfere with their major life activities. Another 13.1 million (5.4 percent of the population) are limited in amount or kind of major activities that they can carry out. The remaining 9.7 million (4.0 percent of the population) are unable to carry on the major activity for someone their age (National Center for Health Statistics, 1989a). The combined prevalence of all three levels of activity limitation increases substantially with age, as shown in Figure 2-1. In 1988, the prevalence of any activity limitation increased from 2.2 percent of children under age 5 to 37.6 percent of adults age 70 or older. The severity of limitation also increases with age, as Figure 2-1 shows. Among people with activity limitations, an increasing proportion in each age group up to age 70 is unable to carry out their major activities (the most severely affected group). After age 70, however, the proportion unable to carry on their major activities decreases, corresponding to the shift in the

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Disability in America: Toward a National Agenda for Prevention FIGURE 2-1 Prevalence of activity limitation due to chronic conditions by degree of limitation and age, 1988. Source: National Center for Health Statistics, 1989a. definition of major activity from work to activities of daily living. Another factor in this pattern is that older people are more likely to reside in nursing homes and similar institutional facilities. Because nursing home residents tend to have more severe activity limitations, adding in the institutionalized population would amplify the trend toward increasing severity of disability with age. Adjusting for the differences in their age distribution, women have slightly lower prevalence rates of activity limitation than men: 12.9 percent vs. 13.2 percent, respectively (National Center for Health Statistics, 1990a). Because women outnumber men in the population and because they have an older age distribution, however, women account for more than 53 percent of the people with activity limitations. Above age 70, women make up 62 percent of the population with activity limitations (National Center for Health Statistics, 1989a). Blacks experience a higher prevalence of activity limitation than whites—16.3 percent for blacks vs. 12.8 percent for whites—when differences in age distributions are taken into account. Furthermore, blacks are likely to experience a greater degree of activity limitation: the proportion unable to carry out their major activities is substantially higher for blacks (6.6 percent) than for whites (3.5 percent) (National Center for Health Statistics, 1990a).

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Disability in America: Toward a National Agenda for Prevention FIGURE 2-2 Prevalence of activity limitation due to chronic conditions, by degree of limitation and family income, 1988. Source: National Center for Health Statistics, 1990a. Activity limitation is substantially more prevalent among people with lower family incomes, as Figure 2-2 shows. The prevalence of activity limitation decreases from 23.2 percent for people with incomes below $13,000 to 8.1 percent for people with annual family incomes above $45,000. The differential is larger for the most severe activity limitations: the proportion of people unable to carry out their major activities decreases from 9.1 percent in the lowest income group to 1.4 percent in the highest income group. Because the institutionalized population tends to have low incomes, adding this group to the NHIS sample would further amplify this differential (National Center for Health Statistics, 1990a). It should be pointed out that the cause of these differentials is not clear. To some extent, people with lower socioeconomic status probably experience more disability just as they experience more injuries, higher mortality rates, less access to health care, and generally poorer health. On the other hand, some people have lower incomes because their disabling conditions restrict their ability to work. Cross-sectional survey data cannot provide any insight into the relative importance of these two very different explanations for the relationship between income and activity limitation.

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Disability in America: Toward a National Agenda for Prevention In general, people with activity limitations are substantially older and poorer than those without limitations. With regard to age, 32 percent of people with activity limitation are over 65, compared with 9 percent of people without limitations. Only 10 percent of the population with activity limitations are under 18, compared with 29 percent of people without limitation. Furthermore, 22 percent of the population with activity limitations—compared with 10 percent of people without limitation—have incomes under $10,000, and 18 percent—compared with 33 percent—have incomes over $35,000. Other Perspectives The NHIS data (National Center for Health Statistics, 1989a) also provide perspectives on aspects of disability beyond activity limitation. For instance, respondents were restricted in activity for an average of 14.7 days in 1988 because of acute and chronic conditions, including an average of 6.3 bed-disability days. Furthermore, 39.1 percent of the respondents rated their own health as "excellent," 27.8 percent as "very good," and 23.2 percent as "good." Only 9.9 percent rated their health as "fair" or ''poor." This is smaller than the proportion—13.7 percent—that experience any activity limitation. As with activity limitation, the proportion of people who rate their health as fair or poor increases with age, decreases with income, and is higher for blacks than for whites. As discussed below, a variety of other surveys and data systems generate estimates of the prevalence of disability. Tables 2-1, 2-2, and 2-3 present some of the measures available from the NHIS and other sources. The target population is usually the civilian noninstitutionalized population, but each study uses different criteria for identifying "disability." Without exception, however, people with disabilities tend to be older, to have less education, and to be poorer than the general population. The ICD survey led to an estimate that about 27 million people, 15 percent of the population age 16 and over, had some disability. Broken down by age in Table 2-1, the prevalence rates are similar to those from the NHIS for the population under age 65. For people 65 and over, however, the NHIS rate is about a third higher. Even though the ICD criteria for disability could be expected to include more people than the NHIS, use of only telephone interviews may have tended to exclude older people with disabilities. Among those included in the ICD survey, 8 percent reported that they experienced no limitation in their activities, and 50 percent did not consider themselves disabled even though they met at least one of the survey's "disability" criteria. However, 46 percent said that they were prevented completely from working, going to school, or keeping house. Two-thirds of the people under age 65 were not working, and two-thirds of the people who were not working reported wanting to work.

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Disability in America: Toward a National Agenda for Prevention TABLE 2-1 Alternative Estimates of Functional and Activity Limitation by Age: United States Survey Under 18 18-44 45-64 65 and Over Numbers (in thousands)         Activity limitation         National Health Interview Survey (1985) 3,221 8,391 10,405 10,709 ICD-Louis Harris (1985) — 8,800a 10,200 8,000 Functional limitation         Survey of Income and Program Participation (1984) 2,326 11,139b 10,541c 15,466 Percent of population group         Activity limitation         National Health Interview Survey (1985) 5.1 8.4 23.4 39.6 ICD-Louis Harris (1985) — 8.2a 22.7 28.0 Functional limitation         Survey of Income and Program Participation (1984) 3.7 10.1b 31.9c 58.7 Notes: Definition of disability differs for each survey. National Health Interview Survey: Unable to carry out major activity; limited in amount or kind of major activity; or limited, but not in major activity. International Center for the Disabled—Louis Harris Survey : Prevented from full participation in work, school, or other activities; having a physical disability, seeing, hearing, or speaking impairment, an emotional or mental disability, or a learning disorder; or considering oneself disabled or considered disabled by others. Survey of Income and Program Participation: For adults, needs assistance with ADLs or IADLS; inability or difficulty in at least one function. For children, having a physical condition that limits the ability to walk, run, or play, or a mental or emotional condition that limits the ability to learn or do school work. a Ages 16-44. b Ages 18-49. c Ages 50-64. SOURCES: National Center for Health Statistics, 1986; Louis Harris and Associates, Inc., 1986; calculated from Rice and LaPlante, 1988a; U.S. Department of Health and Human Services, 1989d. The relationships among a number of different measures of disability are illustrated in Figure 2-3, from the 1984 SIPP. Each box represents a segment of the population (in thousands) meeting a particular combination of conditions. For example, in the bottom right corner 956,000 people are age 65 to 72 and have a work limitation but report no limitations in functioning.

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Disability in America: Toward a National Agenda for Prevention TABLE 2-2 Alternative Estimates of Work Limitation Among Persons Ages 18 to 64: United States Survey Any Work Limit Unable to Work Numbers (in thousands)     National Health Interview Survey (1983-85) 14,347 7,785 Survey of Income and Program Participation (1984) 17,950 8,025 Current Population Survey (1985)a 13,336 6,893 Disability benefit recipients (1984) 4,400 — Percent of population group     National Health Interview Survey (1983-85) 10.1 5.5 Survey of Income and Program Participation (1984) 12.5 5.6 Current Population Survey (1985)a 8.8 4.5 Disability benefit recipients (1984) 3.1 — Notes: Disability Benefit Recipients: Social Security Disability Insurance, Supplemental Security Income, or Veterans Administration benefits. a Ages 16-64. SOURCES: LaPlante, 1988; U.S. Department of Health and Human Services, 1989d; calculated from Haber, 1990, and U.S. Bureau of the Census, 1988. On the basis of functional limitations, the SIPP estimated that 39.5 million people, 17 percent of the noninstitutionalized population, had some degree of disability. (In Figure 2-3, this number is the sum of all numbers in boxes labeled "limitations in functioning," i.e., 2,326 + 9,677 + 8,422 + 3,443 + 118 + 11,310 + 4,157). Another example is work limitations, where the number of persons in the population ages 18-64 with any work limitation totals 17.95 million people (i.e., 8,442 + 3,443 + 549 + 5,515). Table 2-1 shows that the SIPP produced a lower estimate of disability among children than the NHIS. Some of the difference may be due to different types of questions. The SIPP asks a general question on whether any children have limitations, and only with a positive response does it go on to ask which children, up to a total of three. The NHIS includes an individualized inquiry on the presence of activity limitation for each child in the household. For younger adults, the two surveys produce comparable results. At older ages, however, the SIPP shows much higher rates of disability than the NHIS. For people 65 and over, the SIPP rate is half again as high as the NHIS rate. The more extensive questions in the SIPP on the ability to perform specific functions may provide a greater opportunity for respondents to identify limitations.

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Disability in America: Toward a National Agenda for Prevention The SIPP produces estimates of the prevalence of work limitation somewhat higher than those of the NHIS, 18.0 million vs. 14.4 million. Part of this difference may be due to the exclusion of acute conditions as causes of work disability in the NHIS. About 6.4 million of the people with work limitations in the SIPP report no functional limitations, however. Individuals with mental or emotional conditions that limit their ability to work may not have any difficulty with the physical activities that SIPP uses to define functional limitation (U.S. Department of Health and Human Services, 1989d). TABLE 2-3 Alternative Estimates of Degrees of Functional Limitation Among Persons Age 65 and Over: United States   Degree of Limitation Survey More Less Any Numbers (in thousands)       National Health Interview Surveya (1983-1985) ADL/IADL 1,507 2,862 4,369 Survey of Income and Program Participationb (1984) 1,683 2,799 4,482 Long-Term Care Surveyc (1982) 3,384 1,690 5,074 Long-Term Care Surveyc (1984) 3,500 1,965 5,465 Percent of population group       National Health Interview Surveya (1983-1985) ADL/IADL 5.7 10.8 16.5 Survey of Income and Program Participationb (1984) 6.4 10.6 17.0 Long-Term Care Surveyc (1982) 12.7 6.4 19.1 Long-Term Care Surveyc (1984) 12.9 7.2 20.1 Note: ADL = activities of daily living; IADL = instrumental activities of daily living. The activities related to a specific degree of limitation vary among the surveys. "Any" limitation is the sum of the two separate degrees of limitation. a National Health Interview Survey: Major Activity: More = unable to carry out major activity; Less = limited in amount or kind of major activity. ADL/IADL: More = needing assistance in any ADL; Less = needing assistance only in IADLs. b Survey of Income and Program Participation: More = needs assistance with ADLs; Less = needs assistance only with IADLs. c Long-Term Care Surveys: More = any limitations in ADLs; Less = limitations only in IADLs. SOURCES: Calculated from LaPlante, 1988; U.S. Department of Health and Human Services, 1989; Macken, 1986; Manton, 1989.

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Disability in America: Toward a National Agenda for Prevention TABLE 2-5 Years of Expected Life with Activity Limitations Due to Specified Conditions at Birth, at Age 65, and at Age 75: United States, 1987 Condition Years at Birth Years at Age 65 Years at Age 75 All conditions 12.8 6.3 4.6 Mobility limitations 4.7 2.2 1.6 Intellectual impairments 0.9 0.4 0.4 Sensory impairments 1.0 0.6 0.6 Chronic diseases 4.3 2.3 1.6 Other conditions or impairments 1.8 0.7 0.5   SOURCE: Calculated from National Center for Health Statistics, 1990c, and LaPlante, 1988. for blacks than for whites between 1970 and 1980, the expected number of activity-limited years also increased more for blacks. The researchers also note that, although the United States, Canada, and France had similar total life expectancies around 1980, Canadians and the French could expect 2 to 5 additional years free of activity limitation. The life table perspective can also be used to determine the average impact of the conditions that are reported as the main cause of activity limitation. Table 2-5 shows the number of years of activity limitation expected at birth and at ages 65 and 75 that would be attributed to mobility limitations, intellectual impairments, sensory impairments, chronic disease, and other kinds of conditions and impairments. Mobility limitations and chronic diseases account for about 70 percent of the years of activity limitation expected at birth and at older ages. At birth, mobility limitations are a slightly more prominent cause of activity limitation than are chronic diseases (4.7 vs. 4.3 years, respectively), but at age 65 chronic diseases are slightly more prominent than are mobility limitations (2.3 vs. 2.2 years). The conditions that lead to activity limitation differ substantially in the age at which they occur, and hence in the number of years that people live with disabilities associated with them. Disability that begins early in life is most commonly associated with developmental disabilities and mobility limitations caused by injuries. Disability that begins later in life is more commonly associated with chronic diseases and mobility limitations due to arthritis. The relative impact of different disabling conditions on the health of the public is clearly of interest in setting prevention priorities. Although the available data do not allow one to calculate the impact of different underlying causes, the life table analysis presented here can provide a rough approximation of the relative impact of disabilities acquired early

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Disability in America: Toward a National Agenda for Prevention and late in life. For this analysis the committee defined "early in life" as occurring before age 45 and "late in life" as after age 45.6 The results of this calculation are that about 6.1 of the 12.8 years of activity limitation expected at birth—slightly less than half—are due to conditions that had their onset before age 45. Thus, although conditions acquired early in life lead to more years of disability per case, the number of individuals who acquire disabilities after age 45 is much greater. Comparing the two in a life course perspective suggests that, in the aggregate, more years of disability are experienced by people acquiring limitations later in life (after age 45). Thus, despite the length of time that people live with developmental disabilities and mobility limitations due to injuries at early ages, more disability years are experienced by people whose disability appears later in life (after age 45), primarily because of chronic diseases and mobility limitation due to arthritis. The analyses in this section are based on a hybrid analytical approach that mixes current-status activity limitation data with dynamic mortality data. Rogers and colleagues have developed a more sophisticated approach to this issue that makes use of data on transitions into and out of disability, and from one degree of disability to another. Their approach allows them to go beyond general statistics for the population as a whole to estimates of the expected time with different degrees of disability for people who have (or do not have) a disability at a particular age (Rogers, R.G., et al., 1989; Rogers, A., et al., 1989). The method they developed, however, requires data from a panel study of individuals surveyed at two points in time. 6   The committee estimated the relative impact of activity limitations occurring before and after age 45 as follows. Age 45 was chosen as a break point because the calculations required use of an age break available in the tabulated NHIS data. All limitations experienced by people under age 45 clearly were initiated before that age, so every activity-limited year experienced before age 45 was counted in the first category. Next, an assumption was made that X percent of the population in every age group above 45 experiences activity limitations due to conditions arising before age 45, where X is the prevalence of activity limitations in the 18-44 age group. These activity-limited years were added to the number experienced before age 45. The difference between the total number of years with activity limitation and the number attributed to conditions with early onset gives the activity-limited years associated with conditions that were acquired after age 45. This calculation requires two assumptions that are clearly not correct, but which partially counteract one another. First, X—the proportion of the population acquiring an activity limitation before age 45—was estimated by the proportion of the 18-44 age group with a limitation. This is clearly an underestimate because the 18-44 age group includes people who have not yet had a chance to acquire the conditions they might expect to have acquired by age 45. Second, an assumption was made that X percent of the population at every age over 45 has a limitation acquired before age 45. This would only be true if mortality rates were the same for people with and without activity limitations. Because people with activity limitations are likely to have higher mortality rates, the true fraction is likely to be less than X, tending to offset the error caused by the first assumption.

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Disability in America: Toward a National Agenda for Prevention Because disability data of this type for the general population are lacking, the method has only been applied to data on older adults. To make their estimates, Rogers and colleagues used data on ADLs reported by individuals interviewed in both the 1984 Supplement on Aging of the NHIS and the 1986 Longitudinal Study of Aging (LSOA), and they defined "dependence" as requiring assistance with seven ADLs. The researchers found that individuals who were independent at age 70 could expect to live 13.4 years on average and had a life expectancy of 3.4 years in a dependent state (25 percent of their life expectancy). Individuals who were dependent at age 70 had a total life expectancy of 12.5 years and a dependent life expectancy of 6.1 years (49 percent). Rogers and his colleagues also found differences in the active life expectancies of men and women. Among those independent at age 70, men had a lower life expectancy than women (11.3 vs. 15.4 years) but a proportionally shorter dependent life expectancy (18 percent vs. 29 percent of total life expectancy). The same pattern held among people who were dependent at age 70. Men had a 9.9-year life expectancy, 40 percent of which was in a dependent state, and women had a 14.5-year life expectancy, 53 percent of which was in a dependent state (Rogers, R.G., et al., 1989). ECONOMIC COST OF DISABILITY Disability imposes an enormous economic cost on society. It is costly to the nation in terms of the medical resources used for care, treatment, and rehabilitation; in reduced or lost productivity; and in premature death. For example, persons with disabilities use more medical care services than those without them. In 1979, 15 percent of the noninstitutionalized population that was limited in activity due to chronic conditions made 29 percent of the visits to physicians and accounted for 40 percent of the hospitalizations. Persons with activity limitations made 9.5 physician visits per person, compared with about 3.9 visits for persons with no activity limitation (National Center for Health Statistics, 1981a). Those unable to carry on their major activities made 11.9 visits per person per year. The hospitalization rate for those with activity limitations is almost four times that for people with no activity limitations: 38.3 discharges per 100 persons compared with 9.8 per 100, respectively. Not surprisingly, older persons with chronic and disabling conditions are high utilizers of medical resources. The elderly with activity limitation had 8.7 visits to physicians per year, in contrast with 4.3 visits for persons with no activity limitation. They had 41.2 hospitalizations per 100 elderly persons per year, in contrast with 14.8 hospitalizations per 100 people with no limitation of activity. The 46 percent of elderly people who were limited in activity because of a chronic condition accounted for 63 percent of physician

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Disability in America: Toward a National Agenda for Prevention contacts, 71 percent of hospitalizations, and 82 percent of all the days that older people spent in bed because of health conditions (National Center for Health Statistics, 1981a). Among the 1.5 million nursing home residents in 1985, more than four-fifths (82.1 percent) were reported by their next of kin at the time of admission as being dependent in one or more activities of daily living. More than half (50.5 percent) were dependent in four or more ADLs (National Center for Health Statistics, 1989b). In addition, current medical service, social services, and entitlement programs for persons with disabling conditions are not well coordinated at the national and state levels and offer uncertain benefits with regard to restoring persons with disabling conditions to their highest levels of functioning. Assessments of the effectiveness of these programs are largely unsatisfactory because the evaluations usually measure traditional medical outcomes (physiological and biochemical results) rather than quality of life. Health services research is needed for the development and application of improved methodologies to measure the effectiveness of the health and social service systems on maintaining those persons with disabling conditions at maximal functional capacity and quality of life. Several estimates of the high economic costs of disability in the United States are now available. Chirikos (1989) estimates aggregate economic disability losses at $176.8 billion in 1980, as shown in Table 2-6. Included are: net consumption attributable to disability, that is, the difference in medical care utilization and costs before and after the disabling condition occurred. This amounts to $90.6 billion, 51 percent of the total, and includes expenditures for hospital, medical, and institutional care of people with disabilities, paid household work, and non-health-care spending; primary market time, or the value of reduced productivity on the part of persons with chronic disability, valued at $68.4 billion, or 39 percent of the total; and secondary market time, or the value of productivity losses for members of the households of persons with disabilities, valued at $17.7 billion, or 10 percent of the total. Disability losses for males were significantly higher than for females—$115 billion and $62 billion, respectively. Losses for the working population were estimated at $112 billion; losses for dependents were estimated at $65 billion. Berkowitz and Greene (1989) used a different approach for estimating the cost of disability. They estimated disability expenditures in 1986 for the

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Disability in America: Toward a National Agenda for Prevention TABLE 2-6 Disability Losses (in millions of dollars) for the Population Aged 18-64 Years, by Sex and Age, 1980 Age Group Total Males Females Total $176,778 $115,140 $61,638 Working population 111,605 82,680 28,925 15-24 6,726 4,198 2,528 25-44 32,117 23,102 9,015 45-64 72,762 55,380 17,382 Dependents 65,173 32,460 32,713 Under 15 4,206 2,630 1,576 65-74 29,858 18,408 11,450 75 and over 31,109 11,422 19,687   SOURCE: Adapted from Chirikos, 1989. population aged 18 to 64 years to be $169.4 billion, comprising three types of expenditures: transfer payments (transfer of funds from one payer to another in which no new goods or services are produced) amounted to $87.3 billion; included are social insurance programs, individual and employer programs, and income support; medical care expenditures, which amounted to $79.3 billion in 1986; included are expenditures under public programs (Medicare, Medicaid, Department of Defense, Veterans Administration, and Workers' Compensation) and private insurance; and direct service expenditures, which amounted to $2.8 billion; included are expenditures for rehabilitative services, veterans services, services offered to persons with specific impairments, general federal programs, and employment assistance programs (Table 2-7). Berkowitz and Greene (1989) also present disability expenditure trend data. Disability expenditures rose almost ninefold, from $19.3 billion in 1970 to $169.4 billion in 1986; as a percentage of GNP, disability expenditures rose from 1.9 percent in 1970 to 4 percent in 1986 (Figure 2-11). In per capita terms, expenditures rose from $167 to $1,136 during this 16-year period. The largest growth was between 1970 and 1975, when real disability expenditures (adjusted for rising prices) rose 13 percent annually. The second half of the 1970s showed a slowing rate of increase in disability expenditures; the 1980s was a period of contraction in government spending, resulting in an average rate of real growth of 5 percent per year. Berkowitz and Greene conclude the following: "These fluctuations in disability expenditures are not matched by corresponding fluctuations in injuries or diseases.

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Disability in America: Toward a National Agenda for Prevention TABLE 2-7 Disability Expenditures by Type of Expenditure, 1986 Type of Expenditure Amount (millions) Percent Distribution Total $169,407 100.0 Transfer payments 87,319 51.6 Social insurance (OASDIa) 22,474 13.3 Individual and employer-provided insurance 10,840 6.4 Indemnity 44,987 26.6 Income support 9,018 5.3 Medical care expenditures 79,315 46.8 Medicare 8,828 5.2 Department of Defense 108 0.0 Private health insurance 46,043 27.2 Veterans medical care 3,732 2.2 Workers' compensation 4,540 2.7 Medicaid 15,588 9.2 Medical vocational rehabilitation 349 0.2 St. Elizabeth's Hospital 127 0.1 Direct service expenditures 2,773 1.6 Rehabilitative services 1,654 1.0 Veterans 423 0.2 Services to persons with specific impairments 183 0.1 Social Services (Title XX) 355 0.2 Employment assistance programs 158 0.1 a OASDI = Old Age, Survivors, and Disability Insurance. SOURCE: Berkowitz and Greene, 1989. These changes then must be accounted for by demographic changes, changes in social and economic conditions, changes in public perception of disability, and the way that the benefit laws are administered.'' Newacheck and McManus (1988) analyzed data from the 1980 National Medical Care Utilization and Expenditure Survey to obtain data on the use, charges, and financing of medical care for children (under 21 years of age) with disabilities. Total charges for medical care services for children and youth with disabilities, defined as those limited in activity, amounted to $2.4 billion in 1980 and $3.9 billion in 1986 dollars. On a per capita basis, medical expenditures in 1980 amounted to $760 per person limited in activity, almost three times the amount spent by those without limitations. The 4 percent of children and youth who were limited in their activities accounted for 11 percent of total health care expenditures for the under-21 population.

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Disability in America: Toward a National Agenda for Prevention FIGURE 2-11 Estimated value of disability expenditures for 1970 and for 1975-1986. Expenditures in 1986 were more than $169.4 billion. Source: Berkowitz and Greene, 1989. Rice and LaPlante (1988a) also analyzed the 1980 National Medical Care Utilization and Expenditure Survey, focusing on the costs of chronic comorbidity (i.e., more than one condition existing at the same time) for all ages. They estimated that total expenditures for medical care for persons limited in activity amounted to $63 billion in 1980, more than two-fifths of the total medical care expenditures for noninstitutionalized persons (Table 2-8). Persons limited in activity due to one condition incurred medical expenditures of $49.4 billion; for those with two or more conditions, expenditures amounted to $13.6 billion. Sixteen percent of the total noninstitutionalized population with a limiting chronic condition incurred 41 percent of total medical care expenditures (Figure 2-12). On a per capita basis, medical spending amounted to $1,620 per person for those individuals limited by one condition and $2,456 for those persons limited by two or more conditions, compared with $486 for those not limited in activity (Table 2-8). The distribution by age showed that per capita spending for medical care increases with age for those with and without disability. However, there are higher relative differentials in per capita spending between those with limiting conditions and those with none for the under-65 population. Rice and LaPlante (1988b) inflated the 1980 costs of disability to 1987 dollars by the increase in per capita national health expenditures over the 7-year

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Disability in America: Toward a National Agenda for Prevention TABLE 2-8 Total and Per Capita Medical Expenditures in the Noninstitutionalized Population of People With and Without Disability, by Number of Limiting Conditions and Age, 1980           Persons With Disabilities   All Persons Persons Without Disabilities One Condition Two or More Conditions Age and Sex Amount (millions) Per Person Amount (millions) Per Person Amount (millions) Per Person Amount (millions) Per Person All ages $153,863 $691 $90,856 $486 $49,369 $1,620 $13,638 $2,456 Under 65 112,330 568 74,552 433 31,554 1,424 6,223 1,886 Under 19 21,705 319 19,468 300 2,202 734 35a 267a 19-44 50,911 591 36,543 482 12,925 1,371 1,444 1,637 45-64 39,713 911 18,542 588 16,427 1,687 4,744 2,075 65 and over 41,533 1,650 16,303 1,116 17,815 2,144 7,415 3,290 a Indicates that the relative standard error exceeds 30 percent. SOURCE: Rice and LaPlante, 1988a. Reprinted with permission.

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Disability in America: Toward a National Agenda for Prevention FIGURE 2-12 Distribution of population and medical care expenditures by number of limiting conditions, 1980. Source: Rice and LaPlante, 1988b. Reprinted with permission. period and estimated that the medical care costs of disability totaled $117.6 billion in 1987. For those limited by one condition, medical care costs amounted to $92.2 billion; the remaining $25.4 billion are for those with two or more limiting chronic conditions. These cost estimates do not include losses in productivity due to disability (indirect costs), nor do they include transfer payments. Although the above estimates of the costs of disability vary because of the different methodologies employed, it is clear that disability imposes a large economic cost on the public and private sectors of our society. The data show that the economic cost of multiple chronic conditions causing activity limitations is significant and high, a result that is not very surprising because the probability of disability and medical care use is greater for persons with multiple or comorbid conditions regardless of other factors. Thus targeting measures to prevent or reduce disability and its high economic toll is clearly in the nation's interest and should be given high priority. CONCLUSION Disability statistics rely on a wide variety of measures. The general-purpose NHIS data rely primarily on activity limitation as a measure of disability. Other data systems, designed for different purposes, use different measures: work disability, disability compensation, ability to perform particular tasks, and so on. The result is a patchwork of data that reflect the complexity of the concept of disability. Unfortunately, for technical reasons, it is often difficult to compare data from different sources.

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Disability in America: Toward a National Agenda for Prevention Furthermore, unresolved conceptual difficulties in measuring disability can make it difficult to compare and comprehend the implications of existing data. Some clinical measures of functional status, for instance, which were developed to follow individual patients in the course of treatment, are too detailed and require too much medical expertise and/or equipment to be used in a broad-based population survey (Guralnik et al., 1989a). Some issues are difficult to measure through respondents. For instance there can be confusion between one's ability to carry out a specific task and whether one gets assistance in carrying it out (Wilson and Drury, 1984). Just as role expectations influence whether a functional limitation becomes a disability (Nagi, 1965), statistical measures of functional limitation can be affected by what people expect or are expected to be able to do. For instance, if health promotion messages convince an older woman that she should walk more often, a mild case of arthritis that did not limit her activity before could interfere with walking on some days. Despite a probable improvement in health status, she would legitimately then be counted by the NHIS among those with activity limitations. A similar effect explains part of the apparent increase in disability in the 1970s among middle-aged men. Improved chronic disease screening, increased opportunities for disability compensation, and changing societal norms about early retirement allowed many men to enter medical treatment and to retire earlier than had been possible, probably increasing their health prospects and quality of life. In the official statistics, however, it appears that disability has increased (Wilson and Drury, 1984). Given these limitations, it is clear that comprehensive measures of health status and quality of life are needed to understand the full complexity of disability and the factors leading up to it. Such measures have been developed, but they have been applied primarily in clinical studies. Research on their extension to population-based surveys is underway (Erickson et al., 1989). As was apparent in the life table analyses, there are very few data extant on transitions in the disabling process. Although one can estimate on a cross-sectional basis the relationship between chronic conditions and activity limitation in the NHIS, and between different measures of activity limitation and disability in the SIPP, it is not possible to say much about the transitions from particular chronic conditions to particular functional limitations to different types of disability, for example, work disability. To develop efficient prevention programs it is critical to know the likelihood and rate of a large number of these transitions and their associated risk factors. Finally, it is apparent that the available data focus on the chronic health conditions, not on the underlying processes and events that lead to these conditions and ultimately to disability. For instance, intentional and unintentional injuries are a major cause of the mobility limitations that are so

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Disability in America: Toward a National Agenda for Prevention prevalent in young adults, but no data are available to directly tie particular kinds of injuries—motor vehicle accidents or firearm injuries, for instance—to functional limitations or disabilities. This kind of information is clearly needed to develop effective programs for the prevention of disability. In summary, taking into account all of the data discussed above, it is clear that the number of persons with disabilities depends on the definition of disability. Combining the number of noninstitutionalized people with any activity limitation estimated in the NHIS and the population of all ages in nursing homes, it appears that 35 million people live with disabling conditions. SIPP data point to about 46 million people with some type of work or functional limitation. With definitions focused only on inability to work or to carry out other major activities, or on receipt of disability benefits, the number of people with disabilities is substantially smaller. By any definition, however, people with disabling conditions, on average, are older and have lower incomes than others. Because disability has many dimensions, different measurement concepts are necessary. Data are needed on (1) the clinical conditions that lead to functional limitations, (2) the impact of these limitations on the activities that individuals are able to carry out, and (3) the social and economic impacts these individuals experience because of functional limitations. Each of these aspects of disability can legitimately be measured in different ways, and because social programs are tied to some measures of disability, different definitions to match eligibility requirements are necessary. Although it would be extremely costly and technically difficult for any single data system to deal with all of these concepts and measurement systems simultaneously, it is important that attention be paid to improving the quantity, quality, comprehensiveness, and relevance of data on disability in the United States for consumers and for setting policy.