Population and fertility by age and sex for 195 countries and territories, 1950-2017: a systematic analysis for the Global Burden of Disease Study 2017

Abstract

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 underenumeration 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.

Funding: Bill & Melinda Gates Foundation.

Figure 1

Census age patterns for females in 1970 in the USA (A), males in 2001 in Bangladesh (B), females in 1979 in Afghanistan (C), and males in 2010 in Russia (D) Lines show the model posterior and datapoints. Data processing steps are indicated by symbols. The 95% uncertainty interval is shown by light blue shading around the model posterior. PES=post-enumeration survey.

Figure 2

Fit of the GBD Bayesian demographic balancing model for the total population of males and females, from 1950 to 2017, in mainland China (A), India (B), the USA (C), Indonesia (D), Pakistan (E), Brazil (F), Nigeria (G), and Bangladesh (H) The 95% uncertainty interval is shown by light blue shading around the model posterior line. Mainland China excludes Hong Kong and Macao. GBD=Global Burden of Diseases, Injuries, and Risk Factors Study.

Figure 3

Global total fertility rate distributed by maternal age group (A) and number of livebirths by GBD super-region, for both sexes combined (B), 1950–2017 Total fertility rate is the number of births expected per woman in each age group if she were to survive through the reproductive years (10–54 years) under the age-specific fertility rates at that timepoint. GBD=Global Burden of Diseases, Injuries, and Risk Factors Study.

Figure 4

Proportion of the global population accounted for by the GBD super-regions (A) and the annual population growth rates, globally and for the super-regions (B) Data are shown for both sexes combined, from 1950 to 2017. GBD=Global Burden of Diseases, Injuries, and Risk Factors Study.

Figure 5

Global population pyramids for females and males by age, in 1950, 1975, 2000, and 2017

Figure 6

Total fertility rates under age 25 years (A) and total fertility rate over age 30 years (B), in 2017, by location Data are the number of livebirths expected for a hypothetical woman by age 25 years (A) or ageing from 30 to 54 years (B) who survived the age group and was exposed to current ASFRs. ATG=Antigua and Barbuda. FSM=Federated States of Micronesia. Isl=Islands. LCA=Saint Lucia. TLS=Timor-Leste. TTO=Trinidad and Tobago. VCT=Saint Vincent and the Grenadines.

Figure 7

Percentage change in total fertility rates from 1975 to 2017 for women aged 30–54 years (A) and sex ratio at birth in 2017 (B), by location Data are the number of livebirths expected for a hypothetical woman ageing from 30 to 54 years who survived the age group and was exposed to current age-specific fertility rates (A) and the ratio of males to females at birth (B). ATG=Antigua and Barbuda. FSM=Federated States of Micronesia. Isl=Islands. LCA=Saint Lucia. TLS=Timor-Leste. TTO=Trinidad and Tobago. VCT=Saint Vincent and the Grenadines.

Figure 8

Population growth rate from 2010 to 2017, by location ATG=Antigua and Barbuda. FSM=Federated States of Micronesia. Isl=Islands. LCA=Saint Lucia. TLS=Timor-Leste. TTO=Trinidad and Tobago. VCT=Saint Vincent and the Grenadines.

Figure 9

Relationship between total fertility rates and the population growth rate, 2017 Total fertility rate is 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 age-specific fertility rates observed in the year of interest. Each dot represents a single country or territory. A vertical line is shown at the total fertility rate of 2·05, representing the replacement value, and a horizontal line is shown at a population growth rate of zero.

Figure 10

Proportion of the population that is of working age, globally and for GBD super-regions, 1950–2017 Working age is defined as 15–64 years. Data are for both sexes combined from 1950 to 2017. GBD= Global Burden of Diseases, Injuries, and Risk Factors Study.