Volume 54 - Article 30 | Pages 973–986
The ratio of births observed to births needed: An indicator to assess demographic sustainability
By Thomas Spoorenberg, Vegard Skirbekk
Abstract
Background: A stationary population may offer advantages for societal, economic, and ecological sustainability. It requires that the number of births aligns with expected deaths under given mortality patterns. However, reproductive rates such as the TFR are not designed to assess whether the number of births observed is sufficient to replace expected deaths, necessitating direct assessment of birth–death balance for population sustainability.
Objective: We aim to assess whether current fertility levels are sufficient to replace expected deaths using a new demographic indicator, the ratio of births observed to births needed (Bo/Bn).
Methods: We analyze global and regional demographic sustainability from 1950 to 2100 using data from the World Population Prospects 2024. The Bo/Bn ratio is derived from stationary population theory, comparing actual births to those required under given mortality conditions.
Results: Globally, births observed exceeded those needed by 18% in 2025, but this surplus is declining. According to the United Nations medium variant projection, by 2060, global births will be insufficient to replace expected deaths for the first time in modern history. By 2100, births are projected to fall 12% short of the level needed. Regional variation is substantial: Middle and Eastern Africa maintain Bo/Bn ratios above 2.0, while Eastern Asia exhibits a critically low ratio of 0.49. Currently, 43% of the global population live in countries with insufficient births, and this proportion will reach 75% by 2100.
Contribution: The Bo/Bn ratio provides a direct measure of demographic sustainability that complements traditional fertility indicators, offering crucial insights for policy planning in an era of global demographic transition.
Author’s Affiliation
- Thomas Spoorenberg - United Nations, United States of America EMAIL
- Vegard Skirbekk - Universitetet i Oslo, Norway EMAIL
Other articles by the same author/authors in Demographic Research
The emergence of birth limitation as a new stage in the fertility transition in sub-Saharan Africa
Volume 42 - Article 30
Forty years of fertility changes in the Sahel
Volume 41 - Article 46
Fertility compression in Niger: A study of fertility change by parity (1977–2011)
Volume 39 - Article 24
On the masculinization of population: The contribution of demographic development -- A look at sex ratios in Sweden over 250 years
Volume 34 - Article 37
Reconstructing historical fertility change in Mongolia: Impressive fertility rise before continued fertility decline
Volume 33 - Article 29
Is Buddhism the low fertility religion of Asia?
Volume 32 - Article 1
Reverse survival method of fertility estimation: An evaluation
Volume 31 - Article 9
Old age mortality in Eastern and South-Eastern Asia
Volume 29 - Article 38
What can we learn from indirect estimations on mortality in Mongolia, 1969-1989?
Volume 18 - Article 10
Similar articles in Demographic Research
Uncertainty, resilience, and fertility: Perceived capacity to overcome loss of employment and fertility intentions in Sweden, 2021
Volume 53 - Article 31
| Keywords:
economic uncertainties,
fertility decline,
fertility intention,
globalization,
resilience,
Sweden
Trends in Indigenous fertility in Canada, 2001–2021
Volume 53 - Article 6
| Keywords:
Canada,
fertility decline,
indigenous,
low fertility
Fertility decline, changes in age structure, and the potential for demographic dividends: A global analysis
Volume 50 - Article 9
| Keywords:
age structure,
demographic dividend,
demographic transition,
fertility,
migration,
population momentum,
working-age population
The optimal transition to a stationary population for concentrated vitality rates
Volume 50 - Article 6
| Keywords:
adaptation of net reproduction rate,
age-structured optimal control theory,
stationary population,
transitional path
How does the demographic transition affect kinship networks?
Volume 48 - Article 32
| Keywords:
demographic transition,
demographically dense ages,
kinship network,
net reproductive rate,
time-invariant model
Cited References: 7
Download to Citation Manager
PubMed
Google Scholar