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      Dynamics of life expectancy and life span equality

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          Significance

          Why life expectancy and life span equality have increased together is a question of scientific interest. Both measures are calculated for a calendar year and might not describe a cohort’s actual life course. Nonetheless, life expectancy provides a useful measure of average life spans, and life span equality gives insights into uncertainty about age at death. We show how patterns of change in life expectancy and life span equality are described by trajectories of mortality improvements over age and time. The strength of the relationship between life expectancy and life span equality is not coincidental but rather a result of progress in saving lives at specific ages: the more lives saved at the youngest ages, the stronger the relationship is.

          Abstract

          As people live longer, ages at death are becoming more similar. This dual advance over the last two centuries, a central aim of public health policies, is a major achievement of modern civilization. Some recent exceptions to the joint rise of life expectancy and life span equality, however, make it difficult to determine the underlying causes of this relationship. Here, we develop a unifying framework to study life expectancy and life span equality over time, relying on concepts about the pace and shape of aging. We study the dynamic relationship between life expectancy and life span equality with reliable data from the Human Mortality Database for 49 countries and regions with emphasis on the long time series from Sweden. Our results demonstrate that both changes in life expectancy and life span equality are weighted totals of rates of progress in reducing mortality. This finding holds for three different measures of the variability of life spans. The weights evolve over time and indicate the ages at which reductions in mortality increase life expectancy and life span equality: the more progress at the youngest ages, the tighter the relationship. The link between life expectancy and life span equality is especially strong when life expectancy is less than 70 y. In recent decades, life expectancy and life span equality have occasionally moved in opposite directions due to larger improvements in mortality at older ages or a slowdown in declines in midlife mortality. Saving lives at ages below life expectancy is the key to increasing both life expectancy and life span equality.

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          Most cited references81

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          Demography. Broken limits to life expectancy.

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            Spurious regressions in econometrics

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              Diversity of ageing across the tree of life.

              Evolution drives, and is driven by, demography. A genotype moulds its phenotype's age patterns of mortality and fertility in an environment; these two patterns in turn determine the genotype's fitness in that environment. Hence, to understand the evolution of ageing, age patterns of mortality and reproduction need to be compared for species across the tree of life. However, few studies have done so and only for a limited range of taxa. Here we contrast standardized patterns over age for 11 mammals, 12 other vertebrates, 10 invertebrates, 12 vascular plants and a green alga. Although it has been predicted that evolution should inevitably lead to increasing mortality and declining fertility with age after maturity, there is great variation among these species, including increasing, constant, decreasing, humped and bowed trajectories for both long- and short-lived species. This diversity challenges theoreticians to develop broader perspectives on the evolution of ageing and empiricists to study the demography of more species.
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                Author and article information

                Journal
                Proc Natl Acad Sci U S A
                Proc. Natl. Acad. Sci. U.S.A
                pnas
                pnas
                PNAS
                Proceedings of the National Academy of Sciences of the United States of America
                National Academy of Sciences
                0027-8424
                1091-6490
                10 March 2020
                24 February 2020
                24 February 2020
                : 117
                : 10
                : 5250-5259
                Affiliations
                [1] aInterdisciplinary Centre on Population Dynamics, University of Southern Denmark , 5000 Odense, Denmark;
                [2] bLifespan Inequalities Research Group, Max Planck Institute for Demographic Research , 18057 Rostock, Germany;
                [3] cDepartment of International Health, Bloomberg School of Public Health, Johns Hopkins University , Baltimore, MD 21205;
                [4] dLaboratory of Digital and Computational Demography, Max Planck Institute for Demographic Research , 18057 Rostock, Germany;
                [5] eMortality, Health and Epidemiology Unit, Institut National d’Études Démographiques (INED) , 93322 Aubervilliers, France;
                [6] fCenter for Research in Econometric Analysis of Time Series (CREATES), Aarhus University , 8000 Aarhus, Denmark;
                [7] gDuke University Population Research Institute, Duke University , Durham, NC 27708;
                [8] hEmeritus Research Group, Max Planck Institute for Demographic Research , 18057 Rostock, Germany
                Author notes
                1To whom correspondence may be addressed. Email: jmaburto@ 123456sdu.dk or jvaupel@ 123456sdu.dk .

                Contributed by James W. Vaupel, December 12, 2019 (sent for review September 17, 2019; reviewed by Christiaan Monden, Michael Murphy, and Charles Rahal)

                Author contributions: J.M.A. and J.W.V. designed research; J.M.A., F.V., U.B., and S.K. performed research; J.M.A., F.V., U.B., and S.K. contributed new reagents/analytic tools; J.M.A., U.B., and S.K. analyzed data; and J.M.A., F.V., U.B., and J.W.V. wrote the paper.

                Reviewers: C.M., University of Oxford; M.M., London School of Economics; and C.R., University of Oxford.

                Article
                201915884
                10.1073/pnas.1915884117
                7071894
                32094193
                e13e6208-4b82-4cd3-a087-b5178266e1e0
                Copyright © 2020 the Author(s). Published by PNAS.

                This open access article is distributed under Creative Commons Attribution-NonCommercial-NoDerivatives License 4.0 (CC BY-NC-ND).

                Page count
                Pages: 10
                Product
                Funding
                Funded by: EC | H2020 | H2020 Priority Excellent Science | H2020 European Research Council (ERC) 100010663
                Award ID: 716323
                Award Recipient : José Manuel Aburto
                Categories
                Social Sciences
                Social Sciences

                aging,demography,life span variation,mortality,pace and shape

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