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2

Our Aging World

One prominent demographic outcome of the 20th century is the extent of population aging that has resulted from reduced fertility and increased survival. For the first time in history, many societies have the opportunity to age. Accompanying this broad demographic process, however, are other changes—shifting disease profiles, macroeconomic strains, emergent technologies, changing work patterns and social norms—that are difficult for societies to anticipate and plan for. The intersection of such changes with an evolving demographic context may generate unforeseen issues that become the socioeconomic problems of current and future generations.

Although virtually all of the world's populations are becoming older on average, the extent and pace of aging can vary enormously from society to society. Likewise, as noted in Chapter 1, the meaning of the term “elderly” varies as a result of broad national differences in culture, institutions, and health. Indeed, any chronological demarcation of age boundaries is arbitrary and open to dispute on the grounds that it poorly represents the biological, physiological, or even psychological dimensions of the human experience. Attainment of age 85 may be as extraordinary in one nation as it is commonplace in another. Nevertheless, such demarcation is necessary for a descriptive comparison of international aging. In the following pages, therefore, the term “elderly” refers to persons aged 65 and over, and the term “oldest old” refers to those at least 80 years old. 1

1The chronological demarcation of “oldest old” is an arbitrary one. In industrialized nations, the term usually refers to people aged 85 and over, while in less industrialized nations, where life expectancy on average is lower, the term commonly refers to people aged 80 and over.


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Page 30 2 Our Aging World One prominent demographic outcome of the 20th century is the extent of population aging that has resulted from reduced fertility and increased survival. For the first time in history, many societies have the opportunity to age. Accompanying this broad demographic process, however, are other changes—shifting disease profiles, macroeconomic strains, emergent technologies, changing work patterns and social norms—that are difficult for societies to anticipate and plan for. The intersection of such changes with an evolving demographic context may generate unforeseen issues that become the socioeconomic problems of current and future generations. Although virtually all of the world's populations are becoming older on average, the extent and pace of aging can vary enormously from society to society. Likewise, as noted in Chapter 1, the meaning of the term “elderly” varies as a result of broad national differences in culture, institutions, and health. Indeed, any chronological demarcation of age boundaries is arbitrary and open to dispute on the grounds that it poorly represents the biological, physiological, or even psychological dimensions of the human experience. Attainment of age 85 may be as extraordinary in one nation as it is commonplace in another. Nevertheless, such demarcation is necessary for a descriptive comparison of international aging. In the following pages, therefore, the term “elderly” refers to persons aged 65 and over, and the term “oldest old” refers to those at least 80 years old. 1 1The chronological demarcation of “oldest old” is an arbitrary one. In industrialized nations, the term usually refers to people aged 85 and over, while in less industrialized nations, where life expectancy on average is lower, the term commonly refers to people aged 80 and over.

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Page 31 As a backdrop for subsequent chapters, this chapter describes the current demographic situation of the world's elderly and considers how the future situation might evolve. In addition to reviewing numbers and proportions of elderly people around the world, the discussion provides an overview of the dynamics of population aging, the increasingly important influence of changes in mortality at older ages on overall population aging, and the uncertainty such changes may introduce into our best efforts to project the size and composition of tomorrow's older population. NUMBERS AND PROPORTIONS OF ELDERLY Estimates for the year 2000 indicate an aggregate global total of 419 million persons aged 65 and over, 6.9 percent of the earth's total population. As noted in Chapter 1, the net balance of the world's elderly population is currently increasing by more than 750,000 people each month; two decades from now, the increase will likely be 2 million per month. The number of persons aged 65 and over has increased by 289 million since 1950 and by 99 million just since 1990. 2 In 1995, 30 countries had elderly populations of at least 2 million; projections to the year 2030 indicate that more than 60 countries will reach this level. 3 Population aging refers most commonly to an increase in the percentage of all extant persons who have lived to or beyond a certain age. While the size of the world's elderly population has been increasing for centuries, it is only in recent decades that the proportion has caught the attention of researchers and policy makers. Italy was the demographically oldest of the world's major 4 nations in 2000, with more than 18 percent of 2The demographic estimates and projections in this chapter are taken from two sources. Unless otherwise noted, estimates prior to 1990 are from the latest revision of World Population Prospects (United Nations, 1999). Estimates and projections from 1990 onward are from the International Data Base maintained by the International Programs Center, U.S. Bureau of the Census, and supported by the Office of the Demography of Aging, U.S. National Institute on Aging. 3Though these and other projected figures are by no means certain, they may be more accurate than demographic projections of total population because the latter must incorporate assumptions about the future course of human fertility. Short- and medium-term projections of tomorrow's elderly are not contingent upon fertility because anyone who will be aged 65 or over in 2030 has already been born. When projecting the size and composition of the world's future elderly population, human mortality is the key demographic component. As discussed later in this chapter, current and future uncertainties about changing mortality, particularly at the oldest old ages, may produce widely divergent projections of the size of tomorrow's elderly population. 4Some small nations or areas of special sovereignty, such as Monaco, San Marino, and the Isle of Man, have high percentages of elderly among their populations. Monaco's percentage is higher than that of Italy.

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Page 32its population aged 65 and over (compared with 8 percent in 1950). Other notably high levels (17 percent or more) are seen in Sweden, Greece, Belgium, and Japan. The elderly share of total population will increase only modestly in most industrialized nations between 2000 and 2010, and may even dip slightly as a function of the relatively small cohorts born prior to and during World War II. After 2010, the numbers of and percents of elderly should increase rapidly in some countries as the large post-war birth cohorts (the baby boom) begin to reach age 65. Europe has had the highest proportions of population aged 65 and over among major world regions for many decades and should remain the global leader in this regard well into the 21st century (see Table 2-1). TABLE 2-1 Percent Elderly, by Age and Region: 2000 to 2050 Region Year 65 Years and Over 75 Years and Over 80 Years and Over Europe 2000 14.0 5.6 2.8 2015 16.3 7.7 4.3 2030 23.1 10.8 6.3 2050 28.6 15.7 10.2 North America 2000 12.6 6.0 3.3 2015 14.8 6.3 3.8 2030 20.3 9.4 5.4 2050 20.7 11.6 8.0 Oceania 2000 10.2 4.5 2.4 2015 12.7 5.4 3.2 2030 16.3 7.5 4.4 2050 20.0 10.6 6.6 Asia 2000 5.9 1.9 0.8 2015 7.7 2.7 1.3 2030 11.9 4.5 2.2 2050 18.0 8.5 4.9 Latin America/Caribbean 2000 5.5 1.9 0.9 2015 7.4 2.8 1.5 2030 11.6 4.5 2.4 2050 18.1 8.4 4.9 Near East/North Africa 2000 4.3 1.4 0.6 2015 5.2 1.8 0.9 2030 8.1 2.8 1.3 2050 13.3 5.4 2.9 Sub-Saharan Africa 2000 2.9 0.8 0.3 2015 3.1 1.0 0.4 2030 3.7 1.3 0.6 2050 5.3 1.8 0.9 SOURCE: U.S. Bureau of the Census (2000).

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Page 33 Of the 30 nations with populations at least 13 percent elderly in 2000, only 2 (Japan and Uruguay) are non-European. Until recently, Europe also had the highest proportions of population in the most advanced age categories. But by 1995, percentages of population aged 75 and over and 80 and over in North America had surpassed those in Europe as a whole, largely as a result of small European birth cohorts around the time of World War I. By 2015, however, these percents are again expected to be highest in Europe, and in the year 2050, nearly one of every six Europeans is projected to be aged 75 or older. North America and Oceania also have relatively high aggregate percentages of elderly, and these are projected to increase substantially in the coming decades. Levels for 2000 in Asia and Latin America/Caribbean are expected to more than double by 2030, while aggregate proportions of elderly population in sub-Saharan Africa will grow rather modestly as a result of continued high fertility in many nations. Two important factors bear mention when considering aggregate elderly proportions of regional populations. The first is that regional averages often mask great diversity (see Figure 2-1). Bangladesh and Thailand may be close geographically, but they have divergent paths of expected population aging. Likewise, many Caribbean nations have high proportions of elderly population (the Caribbean is the oldest of all developing world regions) in comparison with their Central American neighbors. By the middle of the 21st century, the elderly share of the total population in Italy is projected to exceed 36 percent, significantly higher than the European average in Table 2-1. Second and more important, percentages by themselves may not give a sense of the growth of absolute numbers. Although the change in percent elderly in sub-Saharan Africa from 2000 to 2015 in Table 2-1 is barely perceptible, the size of the elderly population is expected to increase by 50 percent, from 19.3 to 28.9 million people. Sometimes lost amid the attention paid to population aging in Europe and North America is the fact that older populations in developing countries typically are growing more rapidly than those in the industrialized world. 5 As noted earlier, the net balance of the world's elderly population was increasing by more than 750,000 persons each month at the end of the 1990s; 80 percent of this change was occurring in the developing world. Projections to the year 2050 suggest that the growth rate of the elderly in 5The country classification used in this chapter corresponds to that of the United Nations, wherein “more developed” (and its synonyms “industrialized” and “developed”) comprises all nations in Europe (including seven of the former republics of the Soviet Union) and North America, plus Japan, Australia, and New Zealand. The remaining nations of the world are classified as “less developed” (also referred to as “developing”).

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Page 34 ~ enlarge ~ FIGURE 2-1 Mean and range of variation in percent elderly, by region: 2015. SOURCE: U.S. Bureau of the Census (2000).

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Page 35 ~ enlarge ~ FIGURE 2-2 Average annual percent growth of elderly population in developed and developing countries. SOURCE: United Nations (1999). the developing world will remain significantly higher than in today's industrialized countries (see Figure 2-2). Between 2000 and 2050, countries as diverse as Colombia, Liberia, and Malaysia may expect more than a quadrupling of their elderly populations. GROWTH OF THE OLDEST OLD As a result of past fluctuations in fertility and current trends in mortality, age categories within the elderly aggregate may grow at different rates. An increasingly important feature of societal aging is the progressive aging of the elderly population itself. The fastest-growing age segment in many countries is the oldest old. This group currently constitutes more than 20 percent of the aggregate elderly population in industrialized countries (as opposed to about 13 percent in 1950). In the year 2000, nine industrialized nations had oldest old populations in excess of 1 million. While the proportions of oldest old are lower in developing countries, absolute numbers may be quite high. China, for example, was home to approximately 11.5 million oldest old in 2000, more than in any other country of the world. Figure 2-3 shows the estimated percent distribution of the world's population aged 80 and over at the turn of the century. There is substantial international variation in the projected age components of elderly populations. The share of oldest old among all elderly in the United States was 26 percent in 2000 and is expected to be the same by 2030; the flow of baby boom cohorts into the ranks of the elderly after

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Page 36 ~ enlarge ~ FIGURE 2-3 Percent distribution of world population aged 80 and over: 2000. NOTE: Data represent the share of the world's total oldest old in each country or region. Individual countries with 2 percent or more of the total are shown separately. SOURCE: U.S. Bureau of the Census (2000). 2010 will keep the overall elderly population relatively young. Because of differences in past fertility and mortality trends, some European nations will experience a sustained rise in the share of the oldest old among their elderly populations, while others will see an increase during the next two decades and then a subsequent decline. The most striking global increase is likely to occur in Japan; by 2030, nearly 40 percent of all elderly Japanese are expected to be at least 80 years old. Most developing countries should experience modest long-term increases in this ratio. The share of oldest old among the elderly population may not change significantly in some societies, but burgeoning absolute numbers merit attention. In the United States, the oldest old increased from 374,000 in 1900 to more than 9 million today. The static proportion noted above for the United States masks a projected absolute increase of more than 9 million oldest old (see Figure 2-4). Four-generation families are becoming

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Page 37 ~ enlarge ~ FIGURE 2-4 Population aged 80 and over in the United States: 1900 to 2050 (in millions). SOURCES: U.S. Bureau of the Census for 1900-1990, decennial census data; for 2000-2050, “Population Projections of the United States by Age, Sex, Race, Hispanic Origin, and Nativity: 1999 to 2100” (published January 2000) < http://www.census.gov/population/www/projections/natproj.html >. increasingly common (Soldo, 1996; Grundy et al., 1999), and the aging of baby boom cohorts may result in a great-grandparent boom. The demands of the oldest old vis-à-vis policy making should increase markedly in the 21st century as a result of levels of illness and disability much higher than those of other age groups. The numerical growth and increasing heterogeneity of the oldest old compel social planners to seek further health and socioeconomic information about this group. While it may be simplistic to equate the growth of the oldest old with spiraling health care costs (Binstock, 1993), the fact remains that this group consumes disproportionate amounts of health and long-term care services (Suzman et al., 1992). METRICS OF AGING Speed of Aging The transition from a youthful to a more aged society has occurred gradually in some nations, but will be compressed in many others. For instance, it took only a quarter of a century for the proportion of population aged 65 and over in Japan to increase from 7 to 14 percent (see Figure

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Page 38 2-5). A similarly short transition period is projected for China beginning in the year 2000, and for several other East Asian nations, such as South Korea and Thailand, beginning slightly later in the 21st century. These rapid gains will be driven by sharp drops in fertility in recent decades. In ~ enlarge ~ FIGURE 2-5 Speed of population aging (number of years required or expected for percent of population aged 65 and over to rise from 7% to 14%). SOURCE: Kinsella and Gist (1995).

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Page 39 South Korea, for example, the total fertility rate 6 plummeted from 5 children per woman in the late 1960s to less than 1.8 today. The pace of aging in parts of Asia stands in stark contrast to that in some European countries, where the comparable change occurred over a much longer period. The percent elderly among France's population was higher in the mid-1800s than the current percent elderly in a large majority of the world's developing countries. However, today's rapidly aging societies are likely to face the contentious issues related to health care costs, social security, and intergenerational equity that have sparked public debate in Europe and North America. The speed of population aging may even prompt governments to rethink their overall population policies. Singapore, once a prime advocate of fertility reduction, achieved such success in this arena that the declining birth rate became a cause for political and economic concern. Consequently, Singapore's “Stop at 2” (children) policy was modified in 1987 to provide incentives for higher fertility, particularly among better-educated segments of the population (Phillips and Bartlett, 1995). Median Age Another way to look at population aging is to consider a society's median age, the age that divides a population into numerically equal parts of younger and older persons. While nearly all industrialized countries are above the 31-year level, most developing nations have median ages under 25. In some African and South Asian countries in the mid-1990s, half of the entire population was younger than 15, and high numbers of annual births are likely to keep these countries relatively young in the near future. Yet in developing countries such as China, South Korea, and Thailand, where fertility rates have fallen precipitously, median ages are rising rapidly and should exceed 40 by the year 2025. The concept of median age encourages a broader view of population aging that focuses less on the elderly population per se. In many developing countries, the initial effects of population aging will be seen in the relative growth of young and middle-aged adult populations. This implies a shift in overall population age structure, with accompanying changes in labor force characteristics, household/family structure, and disease patterns. On the one hand, the movement of large birth cohorts into the prime working ages represents an opportunity from a business or government planning perspective. As the working-age population swells, it provides a large potential labor force that may serve as a social and tax 6The total fertility rate is defined as the average number of children that would be born per woman if all women lived to the end of their childbearing years and bore children according to a given set of age-specific fertility rates.

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Page 40base for dependents at both ends of the age continuum. Large numbers of workers relative to elderly persons also may provide the incentive to introduce or expand defined-benefit (pay-as-you-go) pension programs. The latter, however, often become unsustainable in the long run as declines in fertility eventually produce shrinking cohorts of new workers (see Chapter 3). And the potential opportunity presented by a large labor force may be confounded by unstable economic growth and job availability. For example, dramatic percentage increases in labor force size are likely to occur in Africa and the Near East during the period 1990-2020, and the aggregate number of potential job seekers will more than double. The percentage increase will be less in other developing regions, but the absolute growth will be enormous. In Asia alone, economies will need to generate more than a billion additional jobs during the next three decades simply to maintain current rates of employment. Head-Count Ratios A second common set of aging indicators includes the aging index and the elderly support ratio, both of which relate the size of one broad age group (or groups) to another. The aging index is usually defined as the number of people aged 65 and over per 100 youths under the age of 15. Changes in this ratio over time simply indicate the shifting balance of children versus elderly within a society. By the year 2030, most developed countries have a projected aging index of at least 100, and several European countries and Japan likely will have indexes in excess of 200. 7 The elderly support ratio typically is construed as the number of people aged 65 and over per 100 persons aged 20-64, the so-called working-age population. This ratio is often combined with a youth support ratio (persons aged 0-19 per 100 persons aged 20-64) to form a total support ratio that provides a rough indication of the number of non-economically active versus economically active persons in a given society. Such aggregate “head count” measures may be broadly useful in thinking about evolving population age structures, and the shifting weight of youth versus elderly in a country such as China can be remarkable (see Figure 2-6). However, measures such as the elderly support ratio also embody questionable assumptions that make them of limited analytical use (see Box 2-1). 7Given its aggregate nature, the aging index may be more useful for examining within-country differences in the level of population aging than for tracking national-level changes. For example, there can be significant differences in the extent of aging between urban and rural areas and among broader regions, especially in large nations such as Brazil. Based on 1991 census data, the overall aging index in Brazil was 14. However, this measure ranged from less than 6 in several northern states of the country to 21 in the state of Rio de Janeiro.

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Page 55 TABLE 2-4 Life Expectancy at Age 65 in Selected Countries, 2000 Men Women Developed Countries Australia 17.5 21.6 Bulgaria 13.4 16.2 Canada 17.1 21.7 France 16.7 21.3 Germany 15.4 19.2 Italy 16.2 20.2 Japan 17.0 21.3 Russia 11.5 15.4 Sweden 16.4 20.3 United Kingdom 15.2 19.1 Developing Countries Brazil 14.1 17.9 China 13.1 15.6 Egypt 10.6 12.9 India 13.3 13.9 Kenya 13.3 15.1 Mexico 14.2 17.0 Peru 15.1 17.3 Thailand 14.2 17.7 Turkey 15.5 18.4 Zimbabwe 10.1 13.8 NOTE: Figures refer to the average number of years of remaining life for an individual who reaches age 65 in the year 2000. SOURCE: Projected by the U.S. Bureau of the Census (2000) based on the most recent data for each country. developed countries have seen reductions in the proportions of deaths from heart disease and stroke since 1950, often accompanied by a reduction in the death rate from these two diseases. Conversely, cancer rates and proportional mortality from neoplasms have generally risen with time, although the trend has varied by disease site. Multiple-decrement life table analyses for selected developed countries have shown that the sharp rise in cancer rates with age implies a doubling of deaths from cancer in some countries during the period 1950-1990 (Myers, 1996). Among older men, deaths have risen for most disease sites, with the notable exception of stomach cancer. For older women, there is concern about skyrocketing rates of lung cancer (Levi et al., 1992; Lopez, 1995) that have resulted from the upsurge in tobacco consumption among women in the 1960s and 1970s. In France, standardized death rates at ages 65-74

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Page 56 for cancers are now higher than for cardiovascular diseases for both men and women (Mesle and Vallin, 1999). Median ages at death for most chronic conditions have increased over time (Myers and Manton, 1987). For example, from 1950 to 1990, the average age at death from heart disease for women in Canada increased by an estimated 7.5 years, of which 5.3 years is attributed to reductions in mortality at age 65 and over. In other words, the increase in life expectancy at older ages during recent decades is the result of reductions in age-specific rates for most major causes of death. Such reductions may result from the delayed onset of disease (due, perhaps, to better health promotion efforts), as well as from prolonged survival with a disease (perhaps reflecting better treatment of existing conditions). The potential for additional years of life with chronic disease raises important issues about the quality of those additional years. Are we living healthier as well as longer lives, or are we spending an increasing portion of our older years with disabilities, mental disorders, and ill health? In aging societies, the answer to this question will have a profound impact on policies regarding national health and long-term care systems, and on the sufficiency of individual and collective retirement savings. As discussed in Chapter 6, the need to better understand trends in and causes of disability, both within and across countries, is a major challenge for gerontological research. While cause-of-death data at older ages are problematic in every country in terms of precision and cross-national comparability, the problems are exacerbated in developing countries by underreporting of deaths, lack of causal information, inaccurate diagnoses, and ethnologic differences. On a broad scale, it appears clear that the general epidemiological transition already experienced in the developed world has occurred or is occurring in many developing nations as well. 11 Data from Taiwan shown in Table 2-5 exemplify the typical epidemiological shift in causes of death. The infectious and parasitic diseases that dominated Taiwanese mortality in the mid-1950s have given way to chronic and degenerative diseases. By 1976, cerebrovascular disease (primarily stroke) and cancers 12 had become the top killers, and the broader cardiovascular disease category—including cerebrovascular, heart, and hypertensive disease)—accounted for nearly 30 percent of all deaths. The role of cardiovascular diseases 11This is not to say that there is a single, linear trajectory to the epidemiological transition. As Frenk et al. (1991) have shown for several Latin American countries, the “typical” stages of epidemiological transition may not follow a sequential order, but may in fact overlap or even reverse direction. 12It should be noted that cancers themselves may be infectious diseases, particularly in developing countries. Pisani et al. (1999) estimate that 16 percent of all cancer deaths worldwide in the early 1990s were due to infectious agents.

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Page 57 TABLE 2-5 Rank Order of the Ten Leading Causes of Death in Taiwan, 1956, 1976, and 1996 1956 1976 1996 1 GDEC a Cerebrovascular disease Malignant neoplasms 2 Pneumonia Malignant neoplasms Cerebrovascular disease 3 Tuberculosis Accidents Accidents 4 Perinatal conditions Heart disease Heart disease 5 Vascular lesions of CNS b Pneumonia Diabetes mellitus 6 Heart disease Tuberculosis Cirrhosis/chronic liver disease 7 Malignant neoplasms Cirrhosis of the liver Nephritis/nephrosis 8 Nephritis/nephrosis Bronchitis c Pneumonia 9 Bronchitis Hypertensive disease Hypertensive disease 10 Stomach/duodenum ulcer Nephritis/nephrosis Bronchitis c a Includes gastritis, duodenitis, enteritis, and colitis (except diarrhea of newborns). b CNS refers to the central nervous system. c Includes emphysema and asthma. SOURCE: Taiwan Department of Health (1997). as the principal cause of death also has been well documented in other parts of Asia (Ruzicka and Kane, 1991) and in a large majority of Latin American and Caribbean countries (Pan American Health Organization, 1998). With regard to causes of death at ages 65 and over, World Health Organization (1998) data for developing countries with reasonably reliable cause-of-death information suggest that more than half of all deaths in the 1990s in numerous nations (e.g., Argentina, Kazakstan, Tajikistan, Uzbekistan) were attributable to cardiovascular disease. The share of cancer deaths among the elderly is between 12 and 25 percent in most cases. RELIABILITY OF DEMOGRAPHIC PROJECTIONS OF THE ELDERLY Tomorrow's elderly, as noted earlier, already have been born, at least until the time horizon reaches the year 2065. Therefore, future fertility rates may affect the proportion of older persons in a given society, but not their number. Current and future mortality trends are of increasing concern to social scientists and policy planners because assumptions about these trends vary considerably and may have surprisingly divergent implications for future programs. Past population projections often have underestimated improvements in mortality rates, particularly among the oldest old. Consequently, global and national projections of the size of older populations generally have missed the mark and regularly have

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Page 58been revised upwards. For example, in its 1980 assessment of world population, the United Nations projected a global total of 760 million elderly (65+) by the year 2025. The latest United Nations (1999) assessment projects 817 million elderly, 57 million and roughly 8 percent more than forecast in 1980. On a national level, consistently low projections of the elderly population poorly serve planning in such areas as health care costs and delivery systems, pension scheme payouts, and housing design. In industrial nations, mortality is now so low among children and young adults that improvements at these ages (except for mortality from violence and HIV/AIDS among young males), even if it occurs, can contribute very little to overall improvements in life expectancy (National Research Council, 2000). Hence, projection “errors” tend to be greatest at older ages. A series of studies by Keilman (cited in Lee and Miller, 2000) has identified systematic underestimation of the elderly population in projections for industrialized countries on the order of .5 percent per year for the elderly and about 1 percent per year for persons aged 85 and over. Over a 75-year period, these errors would compound so that the actual number of elderly could be 60 percent higher than expected, while the 85-and-over population could exceed current projections by 300 percent. Such calculations lead some to argue that the actual numbers of tomorrow's elderly and especially the oldest old could be much higher than presently anticipated (see Box 2-2). Until recently, it was generally assumed that the human death rate increases with age in an exponential manner. Research has now documented that at very old ages, the rate of increase in the mortality rate tends to slow down, 13 and several hypotheses have been advanced as explanations for this phenomenon (see Horiuchi and Wilmoth, 1998, for one discussion of competing explanations). There is no empirical or theoretical basis for assuming that life expectancy will peak at some numerical limit in the future. This is especially so in light of recent medical advances, potential developments in gene therapy, and the realization that the rate of mortality increase in humans slows down at very advanced ages. Methodological issues also are important in this context. Caselli (1996) has explored the usefulness of projecting mortality by cause of death, noting that the results provide a strong basis for implementing health promotion measures. Lee and Tuljapurkar (1998) argue that the usual method for dealing with uncertainty in population projections—i.e., the use of high/medium/low variants—is flawed. They and others (Lutz et al., 1998; National Research Council, 2000) posit that stochastic forecasts based on time series of vital rates offer important advantages, 13This has been demonstrated in nonhuman species as well; see, for example, Carey, 1997; Vaupel et al., 1998.

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Page 59 BOX 2-2 The Proliferation of Centenarians As the average length of life increases, the concept of “oldest old” will change. We now have, for the first time in history, the opportunity to consider significant numeric growth of the population aged 100 and over. While people of extreme old age constitute a very small portion of the total population in most of the world, their numbers are of growing significance, especially in more developed nations. Hence it is increasingly important to have greater age detail about the very old. In the past, comparable population projections for the world's countries often grouped those aged 80 and over into a single open-ended category. Recently, agencies such as the United Nations Population Division and the U.S. Bureau of the Census's International Programs Center have produced or made plans to produce sets of international population projections that expand the range of older age groups to include an open-ended category of age 100 and over. According to researchers in Europe, the number of centenarians has doubled each decade since 1950 in industrialized countries. Using reliable statistics from 10 western European countries and Japan, Vaupel and Jeune (1995) estimated that some 8,800 centenarians lived in these countries as of 1990, and that the number of centenarians grew at an average annual rate of approximately 7 percent between the early 1950s and the late 1980s. They also estimated that over the course of human history, the odds of living from birth to age 100 may have risen from 1 in 20 million to 1 in 50 for females in low-mortality nations such as Japan and Sweden. There are several problems with obtaining accurate age data on very old people (Kestenbaum, 1992; Elo et al., 1996), and estimates of centenarians from censuses and other data sources should be scrutinized carefully. For example, the 1990 U.S. census recorded some 37,000 centenarians. Although the actual figure is thought to be closer to 28,000 because of age misreporting (Krach and Velkoff, 1999), the census figure represents a doubling of the population aged 100 and over from 1980 to 1990, similar to estimates for European nations. The potentially spectacular increase in numbers of centenarians is illustrated by data and projections for France. Dinh (1995) estimated that there were about 200 centenarians in France in 1950, and that by the year 2000 the number would be 8,500. His 50-year projections suggest there will be 41,000 people aged 100 and over by 2025, increasing to 150,000 in 2050. If these projections are realized, the number of centenarians in France will have multiplied by a factor of 750 in one century. SOURCE: Excerpted from U.S. Bureau of the Census (in press). particularly for mortality estimation, 14 and suggest exploring the value of cohort projections of life expectancy. The upshot is that such views, coupled with expectations of future advances in a variety of medical and nonmedical technologies, may lead 14Lee and Tuljapurkar's favored model suggests that future increases in life expectancy in the United States will proceed approximately twice as fast as implied by projections of the U.S. Bureau of the Census and the U.S. Social Security Administration.

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Page 60researchers to very different assumptions about the trajectory of human mortality and the numbers of tomorrow's elderly populations. For example, Figure 2-10 shows forecasts of the size of the U.S. population aged 85 and over through the year 2040, produced by the U.S. Bureau of the Census using two different mortality assumptions. These official projections are contrasted with those made by Guralnik et al. (1988), which show the effect of assuming a continuation of the 2 percent annual decline in death rates experienced during the 1980s. Much more optimistic forecasts of lowered death rates have resulted from mathematical simulations of reductions in known risk factors for chronic diseases, other morbidity, and mortality. One such simulation (Manton et al., 1993) generated an extreme upper bound projection of 54 million people aged 85 and over in the United States in 2040. While this and other projections are perhaps not the most likely, they underscore the potential impact of changes in adult mortality on the future size of the very old population and demonstrate the uncertainty inherent in projections of numbers and age composition. Indeed, this report and its recommendations are motivated in large part by the necessity to know more about health and mortality dynamics in aging populations and to increase our ability to factor uncertainty into program and policy planning. ~ enlarge ~ FIGURE 2-10 Forecasts of the U.S. population aged 85 and over.

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