Population growth was observed in societies with advancing economies. However, over the recent decades, economists and demographers have grown to believe that as societies grow richer and more advanced, birth rates inevitably decline. This trend has been seen in developed countries like the United States and Japan. A newer study showed that this trend is reversible and that there are more specific factors leading to declining birth rates in developed countries.
Breaking the J-Shape: Economic Uncertainty Disrupts Fertility Trends Based on Fertility Trends in the United States
Background
Demographic researcher Mikko Myrskylä introduced the J-shape thesis in a 2009 paper cowritten with colleagues Hans-Peter Kohler and Francesco C. Billari. Their investigation indicated that countries with a high Human Development Index experience a reversal in fertility decline. The trend was illustrated as a curve in the fertility graph that starts at a very high level and falls steeply before rising slowly to form an inverse J.
A more recent study spearheaded by Henrik Alexander Schubert of the Max Planck Institute for Demographic Research with colleagues Christian Dudel, Marina Kolobova, and Mikko Myrskylä, which was published on 1 December 2024 in Demography, revisited the inverse J-shape hypothesis by examining the relationship between human development and fertility rates in the United States from 1969 to 2018 using state-level data.
Schubert et al. employed a longitudinal analysis of state-level fertility trends across 50 states and combined advanced statistical techniques with subnational data to test the inverse J-shape hypothesis. Total fertility rate or TFR was used as the main fertility indicator to capture changes over time. Human Life Indicator or HLI, which captures the average lifespan and lifespan distributor, was the main indicator for human development.
Findings
• Confirmation of the J-shape Thesis: Findings showed an initial decline and later rebound in fertility rates. As human development increased, fertility rates initially decreased but at higher levels of development, fertility rates began to rise again.
• Post-2010 Shift in Fertility Trends: The J-shape weakened after 2010. The previously observed rebound at high development levels became less pronounced or disappeared. The 2007–2008 financial crisis played a major role in disrupting fertility trends. It delayed childbearing and reduced birth rates even in highly developed states.
• Significant Role of Gender Equality: States with higher gender equality experienced less fertility decline compared to those with lower gender equality. Examples include better participation of females in the labor force and parental leave policies.
Takeaways
The findings suggest that periods of high economic uncertainty, such as economic recessions or specific issues like inflation, discourage childbearing and childrearing due to financial instability and overall uncertainties in personal finance. The financial crisis that started between 2007 and 2008 and the subsequent slow recovery contributed to lower fertility rates in the 2010s. This weakened the J-shape pattern.
It is also worth noting that the J-shape pattern was stronger in some states than others. This depends on economic conditions and existing gender equality policies. States with strong economic and social safety nets showed higher resilience in fertility rates than those without. This indicates that localized economic and social policies matter.
Efforts to increase birth rates through financial incentives alone have limited success. The most effective way to sustain fertility rates at high development levels is through policies that reduce economic uncertainty and support gender equality. The post-2010 fertility trend shift also suggests a potential structural change. This warrants more investigation into long-term economic and social influences on fertility.
FURTHER READINGS AND REFERENCES
- Myrskylä, M., Kohler, H.-P., and Billari, F. C. 2009. “Advances in Development Reverse Fertility Declines. In Nature. 460(7256): 741-743. Springer Science and Business Media LLC. DOI: 1038/nature08230
- Schubert, H.-A., Dudel, C., Kolobova, M., and Myrskylä, M. 2024. “Revisiting the J-Shape: Human Development and Fertility in the United States.” In Demography. 61(6): 1949-1973. Duke University Press. DOI: 1215/00703370-11680156