- Email: [email protected]
The emergence of extremely old people: the case of Japan
Experimental Gerontology 38 (2003) 735–739 www.elsevier.com/locate/expgero
The emergence of extremely old people: the case of Japan Jean-Marie Robinea,*, Yasuhiko Saitob, Carol Jaggerc a
INSERM De´mographie et Sante´, Universite´ de Montpellier I et CRLC, Val d’Aurelle, 34298 Montpellier Cedex 05, France b Nihon University, Center for Information Networking, 4-25 Nakatomi-Minami, 359 Saitama-ken Tokorozawa-shi, Japan c University of Leicester, Department of Epidemology and Public Health, 22-28 Princess Road West, LE1 6TP Leicester, UK
Abstract It is acknowledged today that the number of oldest old persons, nonagenarians and centenarians, is increasing rapidly. Analysis of data from Japan, where female life expectancy at birth approaches the assumed limit of 85 years, can provide unique information on whether the rate of these demographic changes is accelerating. Adjusted for the size of the birth cohorts, the centenarian doubling time (CDT i.e. the number of years needed to double the number of centenarians), halved in 29 years. Moreover death rates at 100 years and above show a clear decrease if we exclude males at age 105 and over. q 2003 Elsevier Science Inc. All rights reserved. Keywords: Centenarian; Supercentenarian; Human; Mortality rate; Centenarian doubling time
Contrary to our 1980 – 1990s belief, increase in life expectancy at birth did not show any slow down in the low mortality countries (Oeppen and Vaupel, 2002; White, 2002). Life expectancy at birth kept its steady increase of three months per year and henceforth reached the record value of 84.9 years for Japanese women in 2001 (Ministry of Health and Welfare, 2001). This significant increase did not involve a strong reduction in the dispersion of individual life spans around average values and the survival curves do not appear much more rectangular today than 20 years ago. In particular significant premature mortality still persists before the age of 85 years. It is the emergence of a very old population, made up of people aged 95 years and over, which has allowed life expectancy to go on increasing. In this context, Japan provides a unique opportunity to monitor the emergence of this extremely old population not only because it ranks first in the world for life expectancy at birth, with 78.1 years for males and 84.9 years for females, respectively, but also because Japan is a country with a relatively large population, currently around 130 millions inhabitants, where high quality data on age exist since a national birth registration system (Jin-Shin Koseki) was implemented at the beginning of the Meiji Era. In fact as early as 1872 Japan implemented a national registration system (Jin-Shin Koseki), based on the place of * Corresponding author. Tel.: þ 33-467-61-30-43; fax: þ 33-467-61-3047. E-mail address: [email protected] (J.-M. Robine).
residence at birth and covering the entire population, making data on the number of births available since this date (Statistical Yearbook of the Empire of Japan, various years since 1882). In 1914 a complementary resident registry system, based on the place of residence, was established. It provides the date of birth and a link with the place where the initial birth registration was made. Deaths are reported to the municipality of the place of residence. The birth and death registration system is supplemented by periodic censuses of population starting in 1920.1 Since 1963, a list of centenarians (Ministry of Health and Welfare, 1963 – 2002) has been compiled by municipalities from the resident registration system.2 These data are largely sufficient to explore the increase in the number of centenarians during the last forty years and the change in the death rates at extreme ages (Robine and Saito, 2003).
1. The emergence of centenarians We have already reported the growth in the number of centenarians, persons aged 100 years and over, in Japan 1 Since 1920, censuses took place every five years on October 1 except in 1945. 2 From 1963 to 1967 and 1969 to 1973 the information is listed as of September 30th each year. For 1968, the information is listed as of October 31st. From 1974 to 2001, the list was compiled on September 1st but information is listed as of September 30th each year.
0531-5565/03/$ - see front matter q 2003 Elsevier Science Inc. All rights reserved. doi:10.1016/S0531-5565(03)00100-1
736
J.-M. Robine et al. / Experimental Gerontology 38 (2003) 735–739
Fig. 1. Number of persons 100 years old and over, Japan since 1963, by sex.
from 1963 to 2000. In this section we update the figures to 2002 in order to substantiate previous conclusions on trends. The number of centenarians increased in Japan from 154 in September 1963 (20 men and 134 women) to 13,036 in September 2000 (Robine and Saito, 2003) and further to 17,934 in September 2002 (2875 men and 15,059 women). This increase continue to appear exponential (see Fig. 1), with the number of centenarians increasing by a factor of 116 in 39 years. In fact, behind relatively large yearly fluctuations, the rate of increase itself tends to increase. The crude centenarian doubling time (CDT) (unadjusted for the size of the birth cohort) decreases from nearly 8 years at the beginning of the 1970s to around 4 years at the beginning of the 2000s. One reason for the increase in the number of centenarians is the dramatic increase in the number of births during the last years of the 19th century in Japan, from 569,034 births in 1872 to 1,510,835 births in 1902 (National Institute of Population and Social Security Research, 2000), a factor of 2.7. However, the ratio of centenarians per 10,000 births showed a much greater increase, from 3.5 for the 1873 cohort (1.4 for men and 5.6 for women) to 49.6 for the 1902 cohort (16.3 for men and 84.5 for women).3 Behind large yearly fluctuations, the rate of increase of this ratio is not constant and the fitted trend shows an increase from 6.9% in 1974 to 13.7% in 2002. Fig. 2 shows that the CDT, corresponding to this fitted trend in the rate of increase, decreased from around 10 years in 1973 to close to 5 years by the year 2002 after adjustment for the birth level. Thus similar to other low mortality countries in the 1970s (Vaupel and Jeune, 1995), the CDT in Japan halved in 29 years if the number of births is kept constant at the level of 1873, 3
The number of persons 100 years old for 10,000 births is computed by dividing the number of persons aged 100 years, alive at each successive September 30th, by the number of births which occurred between January first and December 31st, one century before. For instance, the number of persons aged 100 years exactly on September 30th, 2000, is divided by the number of births which occurred in 1900 between January first and December 31st. Thus the ratio computed is not exactly a ratio by cohort of persons reaching his/her 100th anniversary for 10,000 births, but a quite fair estimation of this ratio. The number of births by sex is estimated using a ratio of 105 males for 100 females at birth, ratio which is verified for the years when the detail by sex is available.
Fig. 2. Centenarian doubling time (CDT) in year for the number of persons aged of 100 years: raw data and data adjusted on the birth level of 1873, Japan, 1973–2002.
Fig. 3. Number of persons 110 years old and over, Japan, 1963–2002, by sex. Source: Ministry of Health and Welfare (1963–2002) Zenkoku koureisha meibo (A list of centenarians in Japan).
suggesting a significant acceleration in the emergence of the centenarian population in Japan due to increased survival. Moreover, a similar picture emerges if we consider the population aged 105 years and over or the population of supercentenarians (aged 110 years and over). The number of persons aged 105 years and over increased from 11 in September 1963 (1 man and 10 women) to 850 in September 2002 (127 men and 723 women), a factor of 77 in 39 years. Data for 2001 and 2002 confirm the previous findings of an annual increase of around 17% after adjustment for the size of the birth cohorts (Robine and Saito, 2003). Fig. 3 shows the appearance and sudden rise from the 1990s in the number of supercentenarians, defined as persons having reached their 110th birthday. Since 1983 those celebrating their 110th birthday should have been registered at birth and therefore earlier cases must be considered with the great caution. In September 2002, 23 supercentenarians were living in Japan, 17 females and six males. The number of persons 110 years old per 10,000 births one century before, increased from zero for the 1873 cohort, (0.012 for the 1875 cohort) to 0.116 for the 1892 cohort (see Fig. 4).4 However the series remains too short at present to comment on the shape of this increase. 4
See note 2.
J.-M. Robine et al. / Experimental Gerontology 38 (2003) 735–739
Fig. 4. Number of persons aged 110 years per 10,000 births 110 years before, Japan, 1983–2002.
2. Mortality above the age of 100 years in Japan To make inferences on the trends in mortality rate of centenarians by year requires knowledge of the number of deaths in a given year and the size of the centenarian population. Robine and Saito (2003) calculated these rates approximately but here we argue a more precise method. Since the centenarian population and number of deaths are relatively small, particularly in the earlier years, this might affect the conclusions previously drawn. In order to properly celebrate the birthday of centenarians, the Japanese government, each year since 1963, publishes a list of Japanese aged 99 years or older on the first of
737
September. Persons are ordered according to the age they will be on the 30th of September and counts by age and sex are available for each year. From these counts, one can first estimate the number of centenarians alive on the 30th of September ordered by age. Compared to the target counts, the September counts include an excess consisting of those who will die in September having already reached the age of 100 years or more and those who will die in September in the last month of their 100th year before reaching their 100th birthday. Consequently, one must subtract from the September counts the number of deaths of centenarians (defined as aged 100 and more) occurring during September as well as the number of deaths of people still 99 years on the first of September who died during September before reaching their 100th birthday. The number of deaths of centenarians by age, sex, and month is available for each year but the number of deaths of people still 99 years on the first of September who died during September before reaching their 100th birthday must be estimated. Assuming that birthdays are uniformly distributed across the year, we can assume that one twelfth (1/12) of the 99 years old persons alive on September first were in the twelfth month of their 100th year and that they will reach their 100th anniversary on average by mid September. With the further assumption that deaths are uniformly distributed across the month, one can consider that they contribute one twenty-fourth (1/24) of the deaths of 99 years old persons in September (Graph 1). Consequently, one
Graphic 1. Diagram of Lexis showing that the persons born in September 1899 will contribute for one twenty-fourth (1/24) of the deaths of 99 years old persons in September 1999, assuming that birthdays and deaths are uniformly distributed across the year.
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J.-M. Robine et al. / Experimental Gerontology 38 (2003) 735–739
Fig. 5. Actual and fitted death rate at age 100–104, Japan, since 1973, by sex.
can subtract from the September population counts the number of deaths of centenarians occurring in September and one twenty-fourth of the deaths of 99 years old persons occurring in September, in order to estimate the target counts. The linearity hypotheses assumed in this estimation are ones often used in demographic research and taking a little more or less than one twenty-fourth of the deaths of 99 years old persons would have little impact on the result. In practice, having the information by age and by cohort of birth, we subtract from the September population counts one seventh of the deaths of 99 years old persons, currently being in their one 100th year, occurred in September (see Graph 1 for an example). Using this calculation, Fig. 5 shows the changes in actual and fitted (assuming linear trend) Japanese death rates at age 100 –104 years, by sex, since 1973, when the fluctuations of the death rates have mostly disappeared. For females, the fitted death rate at age 100– 104 clearly decreased from 43% in 1973 to 30% in 1999. For males, the fitted death rate at age 100 – 104 decreased from 48% in 1973 to 35% in 1999. However, for males, a single linear trend over the whole period does not appear to fit the data well. There seems to be evidence that two separate trends fit better with the rate of decrease itself reducing from around 1985. Despite larger fluctuations, Fig. 6 also suggests a decrease for female death rates at age 105 and over from 53% in 1973 to 39% at the end of the 20th century. On the other hand, death rates for males at age 105 and over seem to increase.
3. Mortality above the age of 110 years The number of supercentenarians, even in Japan, is not large enough to allow us to estimate the death rates at age 110 and over. To compute such rates we need to gather data from several countries. It is one of the main goals of the International Database on Longevity (IDL).5 After age 100, death rates fall far below a Gompertz trajectory fitted to data 5
www.supercentenarians.org.
Fig. 6. Death rate at age 105 and over, Japan, 1975–2000, by sex.
before age 85. Alternative trajectories have been proposed to account for the mortality deceleration observed after the age of 85 years in low mortality countries. Some authors have suggested a trajectory tending toward but never reaching a plateau or ceiling of mortality (Thatcher et al., 1998; Thatcher, 1999; Lynch and Brown, 2001), whereas others have suggested that mortality could decline after reaching a maximum (Vaupel et al., 1998). Whether mortality reaches a plateau or declines has important theoretical implications. To study this question, data about mortality after age 110 are needed although presently only a few countries can provide accurate data about the ages of the oldest-old. Japan is among them and contributes to IDL with eleven other countries (Australia, Belgium, Canada, Denmark, England and Wales, Finland, France, the Netherlands, Norway, United States of American and Sweden). Currently the database comprises 493 validated records corresponding to people having reached at least the age of 110 years (International Database on Longevity, 2002). Preliminary analyses using data from 7 then 9 countries show that probabilities of death for ages 110 through 114 fall well below a ceiling of 60% (Robine and Vaupel, 2001, 2002). This result strongly supports the finding that mortality does not increase according to the Gompertz curve at the highest ages and is consistent with a plateau around ages 110– 114. An earlier study, based on less complete data (Vaupel et al., 1998), raises the possibility that mortality may fall after age 115. The number of supercentenarians above age 115 is still very small in IDL to
J.-M. Robine et al. / Experimental Gerontology 38 (2003) 735–739
allow exploring this age range but the number of gathered records is increasing quite rapidly. A puzzling question is to know whether these long lived people—centenarians, semisupercentenarians or supercentenarians—reach 100 years or more simply by chance (Finch and Kirkwood, 2000), because of environmental changes (Robine, 2001, 2003) or because they age slower compared to others. Answering this question could be a long term goal of the IDL database, in collaboration with biologists.
Acknowledgements Financing: Research supported by Nihon University Population Research Institute (NUPRI), Tokyo, Japan and Institut National de la Sante´ et de la Recherche Me´dicale, INSERM, Paris, France (INSERM, ACT vieillissement 2002).
References Finch, C.E., Kirkwood, T.B.L., 2000. Chance, Development and Aging, Oxford University Press, New York. International Database on Longevity (IDL) Report—December 2002. Lynch, S.M., Brown, J.C., 2001. Reconsidering mortality compression and deceleration: an alternative model of mortality rates. Demography 38, 79–95.
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Ministry of Health and Welfare, 2001. Abridged life tables for Japan 2001. Ministry of Health and Welfare, Tokyo, Japan. Ministry of Health and Welfare, 1963–2002. Zenkoku koureisha meibo (A list of centenarians in Japan). Ministry of Health and Welfare, Tokyo, Japan. National Institute of Population and Social Security Research, 2000. Latest Demographic Statistics. NIPSSR, Tokyo, Japan. Oeppen, J., Vaupel, J.W., 2002. Broken limits to life expectancy. Science 296, 1029–1031. Robine, J.-M., 2001. A New biodemographic model to explain the trajectory of mortality. Exp. Gerontol. 36, 899 –914. Robine, J.-M., 2003. Life course, environmental change and life span. Pop. Dev. Rev. 29 (suppl) in press. Robine, J.-M., Saito, Y., 2003. Survival beyond age 100: the case of Japan. Pop. Dev. Rev. 29 (suppl). Robine, J.-M., Vaupel, J.W., 2001. Supercentenarians, slower ageing individuals or senile elderly? Exp. Gerontol. 36, 915–930. Robine, J.-M., Vaupel, J.W., 2002. Emergence of supercentenarians in low mortality countries. N. Am. Actuarial J. 6 (3), 54–63. Thatcher, A.R., Kannisto, V., Vaupel, J.W., 1998. The Force of Mortality at Ages 80 to 120, Odense University Press, Odense. Thatcher, A.R., 1999. The long-term pattern of adult mortality and the highest attained age. J. R. Stat. Soc. A 162, 5– 43. Vaupel, J.W., Jeune, B., 1995. The emergence and proliferation of centenarians. In: Jeune, B., Vaupel, J.W. (Eds.), Exceptional longevity: from prehistory to the present, Odense University Press, Odense, pp. 109– 116. Vaupel, J.W., Carey, J.R., Christensen, K., Johnson, T.E., Yashin, A.I., Holm, N.V., Iachine, I.A., Kannisto, V., Khazaeli, A.A., Liedo, P., Longo, V.D., Zeng, Y., Manton, K.G., Curtsinger, J.W., 1998. Biodemographic trajectories of longevity. Science 280, 855–860. White, K.M., 2002. Longevity advances in high-income countries, 1955– 96. Pop. Dev. Rev. 28, 59– 76.
The emergence of extremely old people: the case of Japan Jean-Marie Robinea,*, Yasuhiko Saitob, Carol Jaggerc a
INSERM De´mographie et Sante´, Universite´ de Montpellier I et CRLC, Val d’Aurelle, 34298 Montpellier Cedex 05, France b Nihon University, Center for Information Networking, 4-25 Nakatomi-Minami, 359 Saitama-ken Tokorozawa-shi, Japan c University of Leicester, Department of Epidemology and Public Health, 22-28 Princess Road West, LE1 6TP Leicester, UK
Abstract It is acknowledged today that the number of oldest old persons, nonagenarians and centenarians, is increasing rapidly. Analysis of data from Japan, where female life expectancy at birth approaches the assumed limit of 85 years, can provide unique information on whether the rate of these demographic changes is accelerating. Adjusted for the size of the birth cohorts, the centenarian doubling time (CDT i.e. the number of years needed to double the number of centenarians), halved in 29 years. Moreover death rates at 100 years and above show a clear decrease if we exclude males at age 105 and over. q 2003 Elsevier Science Inc. All rights reserved. Keywords: Centenarian; Supercentenarian; Human; Mortality rate; Centenarian doubling time
Contrary to our 1980 – 1990s belief, increase in life expectancy at birth did not show any slow down in the low mortality countries (Oeppen and Vaupel, 2002; White, 2002). Life expectancy at birth kept its steady increase of three months per year and henceforth reached the record value of 84.9 years for Japanese women in 2001 (Ministry of Health and Welfare, 2001). This significant increase did not involve a strong reduction in the dispersion of individual life spans around average values and the survival curves do not appear much more rectangular today than 20 years ago. In particular significant premature mortality still persists before the age of 85 years. It is the emergence of a very old population, made up of people aged 95 years and over, which has allowed life expectancy to go on increasing. In this context, Japan provides a unique opportunity to monitor the emergence of this extremely old population not only because it ranks first in the world for life expectancy at birth, with 78.1 years for males and 84.9 years for females, respectively, but also because Japan is a country with a relatively large population, currently around 130 millions inhabitants, where high quality data on age exist since a national birth registration system (Jin-Shin Koseki) was implemented at the beginning of the Meiji Era. In fact as early as 1872 Japan implemented a national registration system (Jin-Shin Koseki), based on the place of * Corresponding author. Tel.: þ 33-467-61-30-43; fax: þ 33-467-61-3047. E-mail address: [email protected] (J.-M. Robine).
residence at birth and covering the entire population, making data on the number of births available since this date (Statistical Yearbook of the Empire of Japan, various years since 1882). In 1914 a complementary resident registry system, based on the place of residence, was established. It provides the date of birth and a link with the place where the initial birth registration was made. Deaths are reported to the municipality of the place of residence. The birth and death registration system is supplemented by periodic censuses of population starting in 1920.1 Since 1963, a list of centenarians (Ministry of Health and Welfare, 1963 – 2002) has been compiled by municipalities from the resident registration system.2 These data are largely sufficient to explore the increase in the number of centenarians during the last forty years and the change in the death rates at extreme ages (Robine and Saito, 2003).
1. The emergence of centenarians We have already reported the growth in the number of centenarians, persons aged 100 years and over, in Japan 1 Since 1920, censuses took place every five years on October 1 except in 1945. 2 From 1963 to 1967 and 1969 to 1973 the information is listed as of September 30th each year. For 1968, the information is listed as of October 31st. From 1974 to 2001, the list was compiled on September 1st but information is listed as of September 30th each year.
0531-5565/03/$ - see front matter q 2003 Elsevier Science Inc. All rights reserved. doi:10.1016/S0531-5565(03)00100-1
736
J.-M. Robine et al. / Experimental Gerontology 38 (2003) 735–739
Fig. 1. Number of persons 100 years old and over, Japan since 1963, by sex.
from 1963 to 2000. In this section we update the figures to 2002 in order to substantiate previous conclusions on trends. The number of centenarians increased in Japan from 154 in September 1963 (20 men and 134 women) to 13,036 in September 2000 (Robine and Saito, 2003) and further to 17,934 in September 2002 (2875 men and 15,059 women). This increase continue to appear exponential (see Fig. 1), with the number of centenarians increasing by a factor of 116 in 39 years. In fact, behind relatively large yearly fluctuations, the rate of increase itself tends to increase. The crude centenarian doubling time (CDT) (unadjusted for the size of the birth cohort) decreases from nearly 8 years at the beginning of the 1970s to around 4 years at the beginning of the 2000s. One reason for the increase in the number of centenarians is the dramatic increase in the number of births during the last years of the 19th century in Japan, from 569,034 births in 1872 to 1,510,835 births in 1902 (National Institute of Population and Social Security Research, 2000), a factor of 2.7. However, the ratio of centenarians per 10,000 births showed a much greater increase, from 3.5 for the 1873 cohort (1.4 for men and 5.6 for women) to 49.6 for the 1902 cohort (16.3 for men and 84.5 for women).3 Behind large yearly fluctuations, the rate of increase of this ratio is not constant and the fitted trend shows an increase from 6.9% in 1974 to 13.7% in 2002. Fig. 2 shows that the CDT, corresponding to this fitted trend in the rate of increase, decreased from around 10 years in 1973 to close to 5 years by the year 2002 after adjustment for the birth level. Thus similar to other low mortality countries in the 1970s (Vaupel and Jeune, 1995), the CDT in Japan halved in 29 years if the number of births is kept constant at the level of 1873, 3
The number of persons 100 years old for 10,000 births is computed by dividing the number of persons aged 100 years, alive at each successive September 30th, by the number of births which occurred between January first and December 31st, one century before. For instance, the number of persons aged 100 years exactly on September 30th, 2000, is divided by the number of births which occurred in 1900 between January first and December 31st. Thus the ratio computed is not exactly a ratio by cohort of persons reaching his/her 100th anniversary for 10,000 births, but a quite fair estimation of this ratio. The number of births by sex is estimated using a ratio of 105 males for 100 females at birth, ratio which is verified for the years when the detail by sex is available.
Fig. 2. Centenarian doubling time (CDT) in year for the number of persons aged of 100 years: raw data and data adjusted on the birth level of 1873, Japan, 1973–2002.
Fig. 3. Number of persons 110 years old and over, Japan, 1963–2002, by sex. Source: Ministry of Health and Welfare (1963–2002) Zenkoku koureisha meibo (A list of centenarians in Japan).
suggesting a significant acceleration in the emergence of the centenarian population in Japan due to increased survival. Moreover, a similar picture emerges if we consider the population aged 105 years and over or the population of supercentenarians (aged 110 years and over). The number of persons aged 105 years and over increased from 11 in September 1963 (1 man and 10 women) to 850 in September 2002 (127 men and 723 women), a factor of 77 in 39 years. Data for 2001 and 2002 confirm the previous findings of an annual increase of around 17% after adjustment for the size of the birth cohorts (Robine and Saito, 2003). Fig. 3 shows the appearance and sudden rise from the 1990s in the number of supercentenarians, defined as persons having reached their 110th birthday. Since 1983 those celebrating their 110th birthday should have been registered at birth and therefore earlier cases must be considered with the great caution. In September 2002, 23 supercentenarians were living in Japan, 17 females and six males. The number of persons 110 years old per 10,000 births one century before, increased from zero for the 1873 cohort, (0.012 for the 1875 cohort) to 0.116 for the 1892 cohort (see Fig. 4).4 However the series remains too short at present to comment on the shape of this increase. 4
See note 2.
J.-M. Robine et al. / Experimental Gerontology 38 (2003) 735–739
Fig. 4. Number of persons aged 110 years per 10,000 births 110 years before, Japan, 1983–2002.
2. Mortality above the age of 100 years in Japan To make inferences on the trends in mortality rate of centenarians by year requires knowledge of the number of deaths in a given year and the size of the centenarian population. Robine and Saito (2003) calculated these rates approximately but here we argue a more precise method. Since the centenarian population and number of deaths are relatively small, particularly in the earlier years, this might affect the conclusions previously drawn. In order to properly celebrate the birthday of centenarians, the Japanese government, each year since 1963, publishes a list of Japanese aged 99 years or older on the first of
737
September. Persons are ordered according to the age they will be on the 30th of September and counts by age and sex are available for each year. From these counts, one can first estimate the number of centenarians alive on the 30th of September ordered by age. Compared to the target counts, the September counts include an excess consisting of those who will die in September having already reached the age of 100 years or more and those who will die in September in the last month of their 100th year before reaching their 100th birthday. Consequently, one must subtract from the September counts the number of deaths of centenarians (defined as aged 100 and more) occurring during September as well as the number of deaths of people still 99 years on the first of September who died during September before reaching their 100th birthday. The number of deaths of centenarians by age, sex, and month is available for each year but the number of deaths of people still 99 years on the first of September who died during September before reaching their 100th birthday must be estimated. Assuming that birthdays are uniformly distributed across the year, we can assume that one twelfth (1/12) of the 99 years old persons alive on September first were in the twelfth month of their 100th year and that they will reach their 100th anniversary on average by mid September. With the further assumption that deaths are uniformly distributed across the month, one can consider that they contribute one twenty-fourth (1/24) of the deaths of 99 years old persons in September (Graph 1). Consequently, one
Graphic 1. Diagram of Lexis showing that the persons born in September 1899 will contribute for one twenty-fourth (1/24) of the deaths of 99 years old persons in September 1999, assuming that birthdays and deaths are uniformly distributed across the year.
738
J.-M. Robine et al. / Experimental Gerontology 38 (2003) 735–739
Fig. 5. Actual and fitted death rate at age 100–104, Japan, since 1973, by sex.
can subtract from the September population counts the number of deaths of centenarians occurring in September and one twenty-fourth of the deaths of 99 years old persons occurring in September, in order to estimate the target counts. The linearity hypotheses assumed in this estimation are ones often used in demographic research and taking a little more or less than one twenty-fourth of the deaths of 99 years old persons would have little impact on the result. In practice, having the information by age and by cohort of birth, we subtract from the September population counts one seventh of the deaths of 99 years old persons, currently being in their one 100th year, occurred in September (see Graph 1 for an example). Using this calculation, Fig. 5 shows the changes in actual and fitted (assuming linear trend) Japanese death rates at age 100 –104 years, by sex, since 1973, when the fluctuations of the death rates have mostly disappeared. For females, the fitted death rate at age 100– 104 clearly decreased from 43% in 1973 to 30% in 1999. For males, the fitted death rate at age 100 – 104 decreased from 48% in 1973 to 35% in 1999. However, for males, a single linear trend over the whole period does not appear to fit the data well. There seems to be evidence that two separate trends fit better with the rate of decrease itself reducing from around 1985. Despite larger fluctuations, Fig. 6 also suggests a decrease for female death rates at age 105 and over from 53% in 1973 to 39% at the end of the 20th century. On the other hand, death rates for males at age 105 and over seem to increase.
3. Mortality above the age of 110 years The number of supercentenarians, even in Japan, is not large enough to allow us to estimate the death rates at age 110 and over. To compute such rates we need to gather data from several countries. It is one of the main goals of the International Database on Longevity (IDL).5 After age 100, death rates fall far below a Gompertz trajectory fitted to data 5
www.supercentenarians.org.
Fig. 6. Death rate at age 105 and over, Japan, 1975–2000, by sex.
before age 85. Alternative trajectories have been proposed to account for the mortality deceleration observed after the age of 85 years in low mortality countries. Some authors have suggested a trajectory tending toward but never reaching a plateau or ceiling of mortality (Thatcher et al., 1998; Thatcher, 1999; Lynch and Brown, 2001), whereas others have suggested that mortality could decline after reaching a maximum (Vaupel et al., 1998). Whether mortality reaches a plateau or declines has important theoretical implications. To study this question, data about mortality after age 110 are needed although presently only a few countries can provide accurate data about the ages of the oldest-old. Japan is among them and contributes to IDL with eleven other countries (Australia, Belgium, Canada, Denmark, England and Wales, Finland, France, the Netherlands, Norway, United States of American and Sweden). Currently the database comprises 493 validated records corresponding to people having reached at least the age of 110 years (International Database on Longevity, 2002). Preliminary analyses using data from 7 then 9 countries show that probabilities of death for ages 110 through 114 fall well below a ceiling of 60% (Robine and Vaupel, 2001, 2002). This result strongly supports the finding that mortality does not increase according to the Gompertz curve at the highest ages and is consistent with a plateau around ages 110– 114. An earlier study, based on less complete data (Vaupel et al., 1998), raises the possibility that mortality may fall after age 115. The number of supercentenarians above age 115 is still very small in IDL to
J.-M. Robine et al. / Experimental Gerontology 38 (2003) 735–739
allow exploring this age range but the number of gathered records is increasing quite rapidly. A puzzling question is to know whether these long lived people—centenarians, semisupercentenarians or supercentenarians—reach 100 years or more simply by chance (Finch and Kirkwood, 2000), because of environmental changes (Robine, 2001, 2003) or because they age slower compared to others. Answering this question could be a long term goal of the IDL database, in collaboration with biologists.
Acknowledgements Financing: Research supported by Nihon University Population Research Institute (NUPRI), Tokyo, Japan and Institut National de la Sante´ et de la Recherche Me´dicale, INSERM, Paris, France (INSERM, ACT vieillissement 2002).
References Finch, C.E., Kirkwood, T.B.L., 2000. Chance, Development and Aging, Oxford University Press, New York. International Database on Longevity (IDL) Report—December 2002. Lynch, S.M., Brown, J.C., 2001. Reconsidering mortality compression and deceleration: an alternative model of mortality rates. Demography 38, 79–95.
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