Don
Hucks

Over the past century one of the most consistently observed demographic trends has been the correlation of decreasing fertility with increasing socio-economic development. Indeed, the majority of the world’s population presently resides in regions with below replacement levels of fertility. The replacement rate is the level of reproduction required to maintain a stable population size and is generally defined as 2.1 (children per woman). Much attention has been paid to the economic and social problems associated with rapid, substantial fertility declines and associated population ageing, especially in parts of Europe and Asia where in recent decades fertility rates have fallen well below replacement levels, a trend some observers have described as both irreversible and economically unsustainable. For example, the fertility rate in Spain was just 1.15 in 1996. In Italy the rate was 1.22 in 1994. In Denmark the rate had declined to 1.38 by 1983.

However, in a paper appearing today in the journal Nature, Mikko Myrskylä and Hans-Peter Kohler, of the University of Pennsylvania, and Francesco Billari, of Bocconi University, suggest that the prescription to the problem of fertility decline in highly developed countries may be, somewhat counter-intuitively, further development.

The researchers evaluated demographic data from 140 countries, most of them tracked since 1975, to correlate fertility rates with a metric known as the Human Development Index, which is extensively employed by the United Nations Development Program. HDI takes into account health, economic, and educational factors. Consistent with earlier observations, the authors report an overall pattern of declining fertility with increasing development, across low to moderately high HDI levels.

They observed a strikingly different pattern, however, with regard to countries at the very highest levels of social and economic development. For most highly advanced countries, fertility appears to bottom out, usually well below replacement level, as HDI approaches 0.9 - HDI of 0.9 corresponds to life expectancy of 75 years; per capita GDP of $25,000 US, adjusted to year 2000 value; and a 0.95 education index, based on literacy and educational enrollment at various levels – but it rebounds as HDI continues to rise above 0.9. In 2005, the mean fertility in countries with HDI between 0.9 and 0.92 was just 1.24. Without in-migration, such a rate would result in halving of a population every 40-45 years – a shockingly abrupt decline, with significant economic and social implications. For countries with an HDI above 0.95, on the other hand, the fertility rate was 1.89, close to the replacement level. At this rate, a modest level of in-migration is sufficient to stabilize population size.

The data show that, for the U.S., fertility reversal occurred in 1976 at a fertility level of 1.74, with HDI of 0.881. By 2005, the U.S. fertility rate had climbed to 2.05 as HDI increased to 0.944. (The U.S. is among a very small number of advanced countries with fertility approximately at or above replacement level.) A number of countries experienced much lower fertility levels before seeing fertility increase with further development. In Spain, the fertility rate increased from 1.15 to 1.33 between 1996 and 2005.  In Italy, fertility increased from 1.22 to 1.32 between 1994 and 2005. In Denmark, the rate increased from 1.38 in 1983 to 1.8 by 2005. These examples are representative of the overall trend in the data, with increases in fertility beginning near the 0.9 HDI threshold. This pattern holds for 18 of 24 countries with HDI greater than 0.9.

“The reversal is occurring across a broad range of different countries, suggesting that this reversal is not due to any specific policy intervention or any specific institutional context,” says co-author Hans-Peter Kohler, Professor of Sociology at the University of Pennsylvania. Kohler says these observations may instead reflect a more general characteristic of very advanced societies. “The commonality among all these countries,” Kohler continues, “is basically… the ability to make families, and having children, compatible with modern lifestyles.”

The authors point to high levels of gender equality and an emphasis on work-family balance as possible key factors in reversing fertility decline. They suggest that countries which lag in these areas may experience ongoing fertility reduction, even as they reach very high levels of development. They suggest this as a possible explanation for the fact that in Japan fertility has continued to plummet, from 1.66 in 1988 to 1.26 in 2005, even as HDI increased from 0.897 to 0.943. South Korea has displayed a similar trend, possibly due to similar cultural influences. This explanation, however, must be taken cautiously, as it would not seem to explain the observed data from places like Australia, Austria, Canada, and Switzerland, all of which have experienced continued fertility declines despite enjoying HDI levels greater than 0.93. The authors say more research is needed, to better understand these half dozen exceptions, and to better characterize the factors behind the predominant trend.

“This paper changes the population forecasting dialogue,” says Warren Sanderson, Professor of Economics and History at Stony Brook University, who was not associated with the study. “Population forecasts will change some,” Sanderson continues, “but even more important will be the changes this paper brings to our understanding of the demographic transition.”

The authors conclude that an appropriate strategy for countering the very low fertility observed in many highly developed countries may include the adoption of policies aimed at further increasing the Human Development Index – that is to say, policies that advance health, education, and standard of living.

REFERENCE:

Mikko Myrskylä, Hans-Peter Kohler, and Francesco C. Billari, “Advances in development reverse fertility declines”, Nature, 6 August 2009 (doi:10.1038/nature08230).

http://dx.doi.org/10.1038/nature08230