Cervellati, Sunde and Zimmermann (2017) argued from a unified growth perspective that the historically high growth of the past 150 years partly reflected one-off mortality and fertility changes, and that as the global demographic transition completes and transitional dynamics fade, growth will rest more exclusively on productivity improvements, while the ongoing transition should raise global savings, accumulate capital, depress returns, and keep real interest rates low. Their framework, however, deliberately omits endogenous savings, physical capital accumulation, shocks, and frontier innovation dynamics, so the medium- and long-run implications for secular stagnation, interest rates, and comparative development remain an open research agenda. The problem is to determine how much of the observed and prospective slowdown in economic growth and real interest rates is attributable to fading transitional demographic dynamics versus productivity and technological change, and whether the world economy's post-transition path is one of secular stagnation or sustained growth. Later literature has quantified parts of this agenda — overlapping-generations models and panel studies attribute a meaningful share of the decline in real rates and output growth to demographics (Eggertsson et al. 2019; Gagnon et al. 2021; Aksoy et al. 2019; Jones 2023; Carvalho et al. 2025) — but the overall demographic-versus-productivity decomposition and the post-transition growth trajectory remain open and actively contested.

Background

Secular stagnation is the hypothesis, first advanced by Alvin Hansen (1939) and revived after the 2008 financial crisis, that mature economies may suffer chronically deficient demand and slow growth because the real interest rate needed to equilibrate savings and investment — the natural (neutral) real rate of interest, often written r∗r^* — has fallen below zero, so that monetary policy constrained by the lower bound on nominal rates cannot restore full employment. The demographic transition is the sustained shift from a regime of high mortality and high fertility to one of low mortality and low fertility that accompanies economic development; it reshapes population growth, age structure, and dependency ratios (the ratio of non-working-age to working-age people), and is the central mechanism in unified growth theory, the class of models — originating with Galor and Weil (2000) — that explains the transition from millennia of Malthusian stagnation to modern sustained growth, with fertility and mortality changes as endogenous driving forces. Cervellati, Sunde and Zimmermann (2017) took this long-run perspective to the secular stagnation debate, which had until then focused on short-run business-cycle mechanisms. They accordingly use 'secular stagnation' in its long-run, real-side sense — persistently low growth together with very low real interest rates arising from an excess supply of capital and declining marginal productivity — and treat the emphasis on exceedingly low (zero or negative) rates and on stabilization policy at the lower bound as going beyond the long-run perspective they take, noting that the focus on low interest rates was not at the core of the original secular stagnation hypothesis; that real-side reading is the one used throughout this statement. Documenting that the economic and demographic transitions proceeded asynchronously across world regions, they argued that high past growth rates were partly the consequence of singular, non-recurrent demographic changes (mortality and fertility declines, expanding education, labor-force participation), that latecomer countries' transitions have supported forerunner economies through globalization and capital flows, and that as more countries complete the transition, global savings will tend to rise, capital will accumulate, marginal products and hence real interest rates will decline, and growth will slow toward a path governed by productivity improvements and technological change at the frontier. Their empirical evidence (hump-shaped effects of life expectancy on education accumulation; age-structure effects on growth) is qualitative with respect to these medium- and long-run implications: the quantitative unified growth framework they use does not model endogenous savings or physical capital accumulation, does not account for shocks and crises, and takes no stance on frontier innovation dynamics, institutions, policy, migration, or the distributional effects of capital flows. Whether productivity growth at the technological frontier will stagnate or accelerate is itself contested — Bloom et al. (2020) document that new ideas are getting harder to find, while others remain optimistic about future innovation. The question is thus what the world's growth and real interest rates will look like once transitional demographic dynamics have faded, and how much of the observed slowdown reflects demography rather than productivity — a question the existing literature has so far approached one channel at a time, mostly through closed-economy or OECD-panel overlapping-generations (OLG) models in which people live for multiple periods and saving behavior varies over the life cycle, rather than through a single long-run treatment of the transition itself.

Problem Statement

Determine, theoretically and quantitatively, how much of the observed and prospective slowdown in economic growth and real interest rates — at the global level and across countries at different stages of the economic and demographic transition — is attributable to the fading of transitional demographic dynamics (mortality and fertility declines, population aging, age-structure change, and the associated human capital accumulation) rather than to productivity growth and technological change; and determine whether, once the global demographic transition is complete and growth depends more exclusively on productivity improvements, the world economy converges to a path of secular stagnation (persistently low growth and low real interest rates, with global excess savings pressing returns on capital downward, as Cervellati, Sunde and Zimmermann (2017) argue qualitatively) or to a path of sustained growth. Because the scope for future productivity change is itself contested and, in the source's own assessment, harder to quantify and predict than the role of demographic factors, this determination cannot rest on a frontier productivity path that is simply assumed: it must state which productivity and innovation trajectories lead to each of the two outcomes, and which of them the long-run evidence supports. The acknowledged limitations of the source's prototype — no endogenous savings or physical capital accumulation, no account of the asynchronous timing of demographic transitions across countries interacting through international capital flows, and no stance on frontier innovation dynamics — mark where a quantitative treatment of this question has to go beyond the available evidence, as does the sensitivity of the conclusions to the contested trajectory of productivity growth at the technological frontier. The task is (i) a quantitative decomposition of the slowdown in economic growth and real interest rates into transitional-demographic and productivity/technological components — covering both the observed and the prospective slowdown, at the global level and, where the data permit, across countries at different stages of the transition — and (ii) a determination of whether the post-transition path is one of secular stagnation or sustained growth, which, because the scope for future productivity change is contested, states which productivity and innovation trajectories lead to each outcome and which of them the long-run evidence supports.

References

  1. Cervellati, Matteo; Sunde, Uwe; Zimmermann, Klaus F. (2017). 'Demographic dynamics and long-run development: insights for the secular stagnation debate'. Journal of Population Economics 30(2): 401–432. DOI: 10.1007/s00148-016-0626-8. https://doi.org/10.1007/s00148-016-0626-8
  2. Hansen, Alvin H. (1939). 'Economic Progress and Declining Population Growth'. American Economic Review 29(1): 1–15; reprinted in The Economics of Population, Routledge (2018), pp. 165–182. DOI: 10.4324/9781351291521-24. https://doi.org/10.4324/9781351291521-24
  3. Galor, Oded; Weil, David N. (2000). 'Population, Technology, and Growth: From Malthusian Stagnation to the Demographic Transition and Beyond'. American Economic Review 90(4): 806–828. DOI: 10.1257/aer.90.4.806. https://doi.org/10.1257/aer.90.4.806
  4. Eggertsson, Gauti B.; Mehrotra, Neil R.; Robbins, Jacob A. (2019). 'A Model of Secular Stagnation: Theory and Quantitative Evaluation'. American Economic Journal: Macroeconomics 11(1): 1–48. DOI: 10.1257/mac.20170367. https://doi.org/10.1257/mac.20170367
  5. Carvalho, Carlos; Ferrero, Andrea; Nechio, Fernanda (2016). 'Demographics and real interest rates: Inspecting the mechanism'. European Economic Review 88: 208–226. DOI: 10.1016/j.euroecorev.2016.04.002. https://doi.org/10.1016/j.euroecorev.2016.04.002
  6. Gagnon, Etienne; Johannsen, Benjamin K.; López-Salido, David (2021). 'Understanding the New Normal: The Role of Demographics'. IMF Economic Review 69(2): 357–390. DOI: 10.1057/s41308-021-00138-4. https://doi.org/10.1057/s41308-021-00138-4
  7. Aksoy, Yunus; Basso, Henrique S.; Smith, Ron P.; Grasl, Tobias (2019). 'Demographic Structure and Macroeconomic Trends'. American Economic Journal: Macroeconomics 11(1): 193–222. DOI: 10.1257/mac.20170114. https://doi.org/10.1257/mac.20170114
  8. Rachel, Łukasz; Summers, Lawrence H. (2019). 'On Secular Stagnation in the Industrialized World'. Brookings Papers on Economic Activity 2019(1) (Spring): 1–76. DOI: 10.1353/eca.2019.0000. https://doi.org/10.1353/eca.2019.0000
  9. Goodhart, Charles; Pradhan, Manoj (2020). 'The Great Demographic Reversal: Ageing Societies, Waning Inequality, and an Inflation Revival'. Springer (Palgrave Macmillan). ISBN 978-3-030-42656-9. DOI: 10.1007/978-3-030-42657-6. https://doi.org/10.1007/978-3-030-42657-6
  10. Bloom, Nicholas; Jones, Charles I.; Van Reenen, John; Webb, Michael (2020). 'Are Ideas Getting Harder to Find?'. American Economic Review 110(4): 1104–1144. DOI: 10.1257/aer.20180338. https://doi.org/10.1257/aer.20180338
  11. Jones, Callum (2023). 'Aging, Secular Stagnation, and the Business Cycle'. Review of Economics and Statistics 105(6): 1580–1595. DOI: 10.1162/rest_a_01177. https://doi.org/10.1162/rest_a_01177
  12. Kopecky, Joseph (2023). 'Population age structure and secular stagnation: Evidence from long run data'. The Journal of the Economics of Ageing 24: 100442. DOI: 10.1016/j.jeoa.2023.100442. https://doi.org/10.1016/j.jeoa.2023.100442
  13. Carvalho, Carlos; Ferrero, Andrea; Mazin, Felipe; Nechio, Fernanda (2025). 'Demographics and real interest rates across countries and over time'. Journal of International Economics 157: 104127. DOI: 10.1016/j.jinteco.2025.104127. https://doi.org/10.1016/j.jinteco.2025.104127
  14. Cervellati, Matteo; Meyerheim, Gerrit; Sunde, Uwe (2023). 'The empirics of economic growth over time and across nations: a unified growth perspective'. Journal of Economic Growth 28(2): 173–224 (online first October 2022). DOI: 10.1007/s10887-022-09216-2. https://doi.org/10.1007/s10887-022-09216-2
  15. Emerson, Patrick M.; Knabb, Shawn D.; Sirbu, Anca-Ioana (2024). 'Does the old-age dependency ratio place a drag on secular growth?'. Economic Analysis and Policy 82: 1056–1070. DOI: 10.1016/j.eap.2024.04.026. https://doi.org/10.1016/j.eap.2024.04.026