Page 102 - IJPS-10-4

International Journal of
Population Studies Mortality shapes population age structures

with the evolution of the underlying standard (stationary) arrangements adjust their parameters based on recent life
age structure. tables and survival conditions. Our findings suggest that
The approach we suggest here is extremely simple: it this practice is correct and should be more widespread.
can be regarded as the static version of the dynamic and Acknowledgments
considerably more complex model we recently proposed to
analyze the combined evolution of the two age structures, None.
the stationary and the observed ones (De Santis & Salinari, Funding
2023). Precisely because of its simplicity, our model has its
limitations, and, in particular, it cannot adequately describe We acknowledge the co-funding from these two sources.
all empirical cases (all countries in all years). What it indicates The first is the Next Generation EU, in the context of the
is the likely direction of future changes: An empirical age National Recovery and Resilience Plan, Investment PE8—
structure that is far from its stationary counterpart will likely Project Age-It: “Aging Well in an Aging Society’. This
tend to get closer to it in the future. The force of attraction resource is co-financed by the Next-Generation EU (DM
exerted by the stationary age structure on the observed one 1557 11.10.2022). The second is the Italian MUR (PRIN
is small but persistent; in the short run, other forces, and 2022–No. 2022CENE9F, “The pre-Covid-19 stall in life
especially fertility variations, may affect the observed age expectancy in Italy: looking for explanations”).
structure in a much stronger way (which explains occasional
cases of poor fit with its stationary counterpart). In the long Conflict of interest
run, the prevailing role of survival emerges. The authors declare no conflict of interest.
5. Conclusion Author contribution
Age structures evolve over time, under the influence of Conceptualization: All authors
fertility, mortality, and migration. Demographers have Formal analysis: All authors
long debated the relative role played by each of these Investigation: All authors
forces, focusing in particular on the variations of the age Methodology: All authors
structure or any of its possible synthetic indicators (average Writing – original draft: Gustavo De Santis
age, OADI, etc.). The conclusion has frequently been that Writing – review & editing: All authors
fertility is the main driving force of change, although with
exceptions among mature populations, where mortality Ethics approval and consent to participate
matters more. In this paper, we focus on the shape of Not applicable.
the age structure and we show how close it is to that of
the corresponding stationary population; therefore, we Consent for publication
conclude that mortality (or, better yet, its complement: Not applicable.
survival) plays a significant role in shaping age structures.
We reached this conclusion by combining data from Availability of data
several countries over several periods. Although there are The data used in this study are accessible to the public.
variations and exceptions, the general scheme seems to
hold: observed age structures tend to follow the path traced Further disclosure
by their standards, that is, the corresponding stationary Some findings of this study were presented at a congress
populations. (Population Days, AISP [Associazione Italiana per gli Studi
This finding has both theoretical and practical implications. di Popolazione] held in Rome, Italy, 1-3 January 2023.
Theoretically, this study contributes to the debate on the
relative importance of the forces that drive population aging. References
Our interpretation is that, in the long run, due to its relatively Bengtsson, T., & Scott, K. (2005). Why is the Swedish population
modest but consistent and persistent action, mortality matters ageing? What we can and cannot do about it. Sociologisk
more than anything else, and that recent mortality is generally Forskning, 3:3-12.
enough to “explain” a large fraction of the observed age Bengtsson, T., & Scott, K. (2010). The Ageing Population. In:
distribution of any population at any time. Bengtsson, T., (ed.). Population Ageing-A Threat to the

Regarding practical implications, our findings may be Welfare State. Berlin: Springer Verlag, p.7-22.
relevant, especially in the pension debate. Most pension Borgan, Ø., & Keilman, N. (2019). Do Japanese and Italian

Volume 10 Issue 4 (2024) 96 https://doi.org/10.36922/ijps.377