There has been a remarkable global decline in the number of children women are having, say researchers. Fertility rate falls meant nearly half of countries were now facing a "baby bust" – meaning there are insufficient children to maintain their population size. The researchers said the findings were a "huge surprise". And there would be profound consequences for societies with "more grandparents than grandchildren".
The study followed trends in every country from 1950 to 2017. In 1950, women were having an average of 4.7 children in their lifetime. The fertility rate all but halved to 2.4 children per woman by last year. But that masks huge variation between nations.
The fertility rate in Niger, west Africa, is 7.1, but in the Mediterranean island of Cyprus women are having one child, on average. In the UK, the rate is 1.7, similar to most Western European countries.
The total fertility rate is the average number of children a woman gives birth to in their lifetime (it's different to the birth rate which is the number of children born per thousand people each year). Whenever a country's rate drops below approximately 2.1 then populations will eventually start to shrink (this "baby bust" figure is significantly higher in countries which have high rates of death in childhood). At the start of the study, in 1950, there were zero nations in this position, the report says.
Professor Christopher Murray, the director of the Institute for Health Metrics and Evaluation at the University of Washington, is quoted in the report as saying: "We've reached this watershed where half of countries have fertility rates below the replacement level, so if nothing happens the populations will decline in those countries. It's a remarkable transition. It's a surprise even to people like myself, the idea that it's half the countries in the world will be a huge surprise to people."
More economically developed countries including most of Europe, the US, South Korea and Australia have lower fertility rates.
The report says it does not mean the number of people living in these countries is falling, at least not yet as the size of a population is a mix of the fertility rate, death rate and migration. It can also take a generation for changes in fertility rate to take hold. But Murray said: "We will soon be transitioning to a point where societies are grappling with a declining population." Half the world's nations are still producing enough children to grow, but as more countries advance economically, more will have lower fertility rates.
The report says the fall in fertility rates is not down to sperm counts or any of the things that normally come to mind when thinking of fertility. Instead it is being put down to three key factors: fewer deaths in childhood meaning women have fewer babies; greater access to contraception; and more women in education and work
In many ways, falling fertility rates are a success story, the report says. Without migration, countries will face ageing and shrinking populations. Dr George Leeson, director of the Oxford Institute of Population Ageing, says that does not have to be a bad thing, as long as the whole of society adjusts to the massive demographic change.
He said in the report: "Demography impacts on every single aspect of our lives, just look out of your window at the people on the streets, the houses, the traffic, the consumption, it is all driven by demography. Everything we plan for is not just driven by the numbers in the population, but also the age structure and that is changing, so fundamentally we haven't got our heads around it." He thinks workplaces are going to have to change and even the idea of retiring at 68, the current maximum in the UK, will be unsustainable.
The study, part of the Global Burden of Diseases analysis, says affected countries will need to consider increasing immigration, which can create its own problems, or introducing policies to encourage women to have more children, which often fail.
Report author Murray argues: "On current trends there will be very few children and lots of people over the age of 65 and that's very difficult to sustain global society. Think of all the profound social and economic consequences of a society structured like that with more grandparents than grandchildren. I think Japan is very aware of this, they're facing declining populations, but I don't think it's hit many countries in the West, because low fertility has been compensated with migration. At a global level there is no migration solution." But while the change may challenge societies, it may also have environmental benefits given the impact of our species.
This year's Global Burden of Disease study includes more than 38bn estimates of 359 diseases and injuries and 84 risk factors in 195 countries and territories. And Medical Xpress reports that this version of the GBD study marks the first time the study has produced its own population and fertility estimates. The global population increased by 197% since 1950, from 2.6bn to 7.6bn in 2017.
"To our knowledge, this is the first study to provide transparent and replicable estimates of population and fertility that can be used to inform decision-making and to monitor nations' economic progress," Murray said. "Although total fertility rates are decreasing, the global population continues to grow as death rates decline and because of population 'momentum' in previous decades."
From 2007 to 2017, the world's population has grown annually by 87.2m people, compared with 81.5m annually from 1997 to 2007. In 1950, high-income countries accounted for 24% of the global population, but in 2017, the population of these countries accounted for 14%.
Among countries whose populations grew annually more than 2% from 2010 to 2017, 33 were in sub-Saharan Africa. In addition to Niger, those nations include Nigeria, Ethiopia, and Mali.
Outside of Africa, India, Pakistan, Papua New Guinea, and Haiti are among others with growing populations. By comparison, 33 countries had declining populations between 2010 and 2017, most of which were located in Central, Eastern, and Western Europe – including Georgia, Poland, Romania, Greece, Spain, Portugal – as well as Japan, Cuba, and Puerto Rico.
Summary
Background: Population estimates underpin demographic and epidemiological research and are used to track progress on numerous international indicators of health and development. To date, internationally available estimates of population and fertility, although useful, have not been produced with transparent and replicable methods and do not use standardised estimates of mortality. We present single-calendar year and single-year of age estimates of fertility and population by sex with standardised and replicable methods.
Methods: We estimated population in 195 locations by single year of age and single calendar year from 1950 to 2017 with standardised and replicable methods. We based the estimates on the demographic balancing equation, with inputs of fertility, mortality, population, and migration data. Fertility data came from 7817 location-years of vital registration data, 429 surveys reporting complete birth histories, and 977 surveys and censuses reporting summary birth histories. We estimated age-specific fertility rates (ASFRs; the annual number of livebirths to women of a specified age group per 1000 women in that age group) by use of spatiotemporal Gaussian process regression and used the ASFRs to estimate total fertility rates (TFRs; the average number of children a woman would bear if she survived through the end of the reproductive age span [age 10–54 years] and experienced at each age a particular set of ASFRs observed in the year of interest). Because of sparse data, fertility at ages 10–14 years and 50–54 years was estimated from data on fertility in women aged 15–19 years and 45–49 years, through use of linear regression. Age-specific mortality data came from the Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2017 estimates. Data on population came from 1257 censuses and 761 population registry location-years and were adjusted for under-enumeration and age misreporting with standard demographic methods. Migration was estimated with the GBD Bayesian demographic balancing model, after incorporating information about refugee migration into the model prior. Final population estimates used the cohort-component method of population projection, with inputs of fertility, mortality, and migration data. Population uncertainty was estimated by use of out-of-sample predictive validity testing. With these data, we estimated the trends in population by age and sex and in fertility by age between 1950 and 2017 in 195 countries and territories.
Findings: From 1950 to 2017, TFRs decreased by 49·4% (95% uncertainty interval [UI] 46·4–52·0). The TFR decreased from 4·7 livebirths (4·5–4·9) to 2·4 livebirths (2·2–2·5), and the ASFR of mothers aged 10–19 years decreased from 37 livebirths (34–40) to 22 livebirths (19–24) per 1000 women. Despite reductions in the TFR, the global population has been increasing by an average of 83·8 million people per year since 1985. The global population increased by 197·2% (193·3–200·8) since 1950, from 2·6 billion (2·5–2·6) to 7·6 billion (7·4–7·9) people in 2017; much of this increase was in the proportion of the global population in south Asia and sub-Saharan Africa. The global annual rate of population growth increased between 1950 and 1964, when it peaked at 2·0%; this rate then remained nearly constant until 1970 and then decreased to 1·1% in 2017. Population growth rates in the southeast Asia, east Asia, and Oceania GBD super-region decreased from 2·5% in 1963 to 0·7% in 2017, whereas in sub-Saharan Africa, population growth rates were almost at the highest reported levels ever in 2017, when they were at 2·7%. The global average age increased from 26·6 years in 1950 to 32·1 years in 2017, and the proportion of the population that is of working age (age 15–64 years) increased from 59·9% to 65·3%. At the national level, the TFR decreased in all countries and territories between 1950 and 2017; in 2017, TFRs ranged from a low of 1·0 livebirths (95% UI 0·9–1·2) in Cyprus to a high of 7·1 livebirths (6·8–7·4) in Niger. The TFR under age 25 years (TFU25; number of livebirths expected by age 25 years for a hypothetical woman who survived the age group and was exposed to current ASFRs) in 2017 ranged from 0·08 livebirths (0·07–0·09) in South Korea to 2·4 livebirths (2·2–2·6) in Niger, and the TFR over age 30 years (TFO30; number of livebirths expected for a hypothetical woman ageing from 30 to 54 years who survived the age group and was exposed to current ASFRs) ranged from a low of 0·3 livebirths (0·3–0·4) in Puerto Rico to a high of 3·1 livebirths (3·0–3·2) in Niger. TFO30 was higher than TFU25 in 145 countries and territories in 2017. 33 countries had a negative population growth rate from 2010 to 2017, most of which were located in central, eastern, and western Europe, whereas population growth rates of more than 2·0% were seen in 33 of 46 countries in sub-Saharan Africa. In 2017, less than 65% of the national population was of working age in 12 of 34 high-income countries, and less than 50% of the national population was of working age in Mali, Chad, and Niger.
Interpretation: Population trends create demographic dividends and headwinds (ie, economic benefits and detriments) that affect national economies and determine national planning needs. Although TFRs are decreasing, the global population continues to grow as mortality declines, with diverse patterns at the national level and across age groups. To our knowledge, this is the first study to provide transparent and replicable estimates of population and fertility, which can be used to inform decision making and to monitor progress.
Authors
GBD 2018 Population and Fertility collaborators
[link url="https://www.bbc.com/news/health-46118103"]BBC News report[/link]
[link url="https://medicalxpress.com/news/2018-11-baby-boom-nations-childbirth-vary.html"]Medical Xpress report[/link]
[link url="https://www.thelancet.com/gbd"]The Lancet Global Burden of Disease study[/link]
[link url="https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(18)32278-5/fulltext"]The Lancet article summary[/link]