A New Baby Boom?

Demographer Hans-Peter Kohler sees a rise in fertility in highly developed countries.
October 1, 2009

One of the most established and accepted standards in the social sciences is that human fertility levels tend to decline as countries advance toward higher levels of social and economic development. But a new paper by Professor of Sociology Hans-Peter Kohler, former demography graduate student Mikko Myrskylä, and Francesco Billari, a professor of demography at the Università Bocconi, challenges this conventional wisdom. (Myrskylä, who graduated this past summer, is now head of the research group on lifecourse dynamics and demographic change at the Max Planck Institute for Demographic Research.) Published this August in the journal Nature, the paper reaffirms that fertility does decline when countries at low and medium levels of development continue to develop. However, the researchers found that in highly developed countries, further development can reverse the declining trend in fertility.

The relationship between fertility rates and development has been a long-standing topic in demography and economics, driven initially by concerns about population growth and then about the social and economic problems associated with the emergence of very low fertility (e.g. shrinking labor forces and strained pension systems). Kohler and Billari, longtime collaborators who met when they too worked at the Max Planck Institute, also wrote papers echoing prevailing ideas on the issue.

"The main thing we can say at this point is that countries should develop in a way that allows for a better combination of human capital accumulation, labor force participation and having children." – Hans-Peter Kohler

“We also thought that this decline in fertility rates would be very persistent and unlikely to reverse,” Kohler says. “We’re updating our own findings as well as those of others.” They were able to revisit the topic so fruitfully in part because Billari spent time at Penn last year under the Distinguished International Scholars Program. “The ability to have day-to-day interactions with your colleagues is crucial in research,” Kohler explains.

The researchers conducted both cross-sectional and longitudinal comparisons of total fertility rates (TFR) and the human development index (HDI) for 24 developed countries. (The HDI is the primary index used by the United Nations Development Programme to monitor and evaluate broadly defined human development, based on indicators of a country’s health conditions, living standards and human capital.) In addition to presenting a descriptive analysis of the pattern, the researchers also developed a statistical model that ascertained that the findings were significant.

Although the reversal in TFR decline is common across most of the highly advanced countries, Kohler explains that there is enormous variation in this pattern. On one extreme, the United States—which reached its lowest TFR of around 1.8 children per woman in the mid-1970s—now has a TFR of 2.1, considered the replacement rate. On the other extreme, Italy, which in the 1990s had an extremely low TFR of 1.2, now only has a TFR of 1.3.

“In considering long-term implications, the difference between 1.3 and 2.1 is substantial if you look at what this does to population growth and the age structure of the population,” Kohler says. “We would not make the prediction right now that the Italian fertility rate or that of other countries on the low end of the spectrum would go back to the replacement level anytime soon. Countries like the U.S. are likely to grow, but for countries like Italy, the optimistic thought is, well, they are not shrinking as quickly. But it’s erroneous to think that population aging is no longer a concern or will no longer be an important factor in demographic change.”

Because the reversal trend is so heterogeneous, Kohler also cautions against one-size-fits-all policy recommendations to encourage increases in TFR. He says that far more research must be done to understand the underlying reasons for rising TFRs, especially because the pattern is occurring in countries with very different approaches to family and population policy.

“The U.S. for example has a very hands-off approach, and if you look at state support for families, it probably ranks very low,” Kohler says. “On the other hand, a country like Norway has a very generous welfare state, including many provisions and services for families. The idea of our paper is to stimulate research that would look at what is driving this reversal, and if and how policy has had a role in this reversal, or if it is something that would have occurred with a much more passive hand.”

Three highly advanced countries examined in the study continued to show declines in TFR—South Korea, Japan and Canada. Although the Canadian exception remains a mystery, the paper posits that a paucity of institutions to accommodate the competing demands of earning income—with both men and women participating in the labor force—and having children might account for the negative HDI-fertility relationship in South Korea and Japan.

“The main thing we can say at this point,” Kohler explains, “is that countries should develop in a way that allows for a better combination of human capital accumulation, labor force participation and having children. It’s speculation right now, but governments might explicitly address fertility decline with policies targeted at improving work-family balance and gender equality.”