Fertility, Mortality and Migration

People are born, people move, and people die. Not to be too morbid (there's a lot more to life in between!), but these three things we can be sure everyone does. In fact, on a global scale, these three things can show us fascinating trends in society and the ever-changing makeup of humanity that all of us are part of. In this explanation, we will look at how fertility, mortality, and migration change our world.

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Table of contents

    Fertility, Mortality, and Migration Demography

    Fertility, mortality, and migration determine the population of a country. These three factors can give us insight into where a population is heading, how developed the country is, how the economy is doing, and how desirable of a place it is to live. Through these demographic indicators, we can even explain many cultural, economic, and political issues countries may be facing.

    Demographic Forecasting of Mortality, Fertility, Migration, and Population Data

    The global population is expected to hit 8 billion in 2022. Where will most of those people be born? Many will be born in less developed countries in Asia and Africa. While these countries experience exponential population growth, many highly economically-developed countries are starting to see a decline in population. Why might this be? As countries develop economically, mortality rates decline as the quality of life rises, but fertility rates also start to fall. This is often due to a range of social and economic factors.

    Fertility, Mortality and Migration World Population Projection Pyramid StudySmarterFig. 1 - World Population Projection Pyramid

    Furthermore, the more a country develops, generally the more attractive it is to live there, More immigrants will migrate there, and fewer emigrants will leave. People living longer and not as many being born in the country, and more people moving to the country from elsewhere leads to shifts in the demographic makeup of a country. Demographics are everchanging, and they can explain many things in our world, from economics to political issues, by looking at the cultural and generational distribution of the people who make up the country.

    A good model for seeing the basic format countries follow on the path of development is the democratic transition model.

    Fertility, Mortality and Migration The Demographic Transition Model StudySmarterFig. 2 - The Demographic Transition Model

    The demographic transition model shows five stages of how a population may evolve over time in terms of the proportion of the population in each age group. A country moves into the next stage of this model through economic development.

    The five blue and pink graphs at the bottom are representative population pyramids of how one might expect the distribution of age of the population to look at each stage. Men are represented in blue, and women in pink. The graphs show the population of young people at the bottom and older people at the top. We can see in the first pre-industrial stage a large youth population and a very small elderly population. As a country moves through the stages over the course of decades or even centuries, the age of the population starts to even out, then may even become top-heavy as fertility rates drop.

    The fifth and final stage is about the future projections of fertility rates. It is possible that fertility rates may pick up again as countries recognize the issues of population decline and enact policies to ease the burden of balancing a career with the high time and monetary expense of raising children. For example, affordable child care or government services can increase fertility.

    Fertility Definition

    Fertility, in its simplest definition, is the ability to have children.

    Regarding demography, we will refer to fertility as the fertility rate, how many children, on average, a woman will have in her lifetime. Fertility rates are based on four factors: favorable social norms, flexible labor markets, cooperative fathers, and family policies.1

    Favorable social norms typically involve flexibility in traditional gender roles to fit mothers who want to have a family and a career.

    Flexible labor markets can mean not having repercussions for taking a career break to start a family. Tight labor markets are favorable, meaning jobs are plentiful, as high unemployment can make those employed hesitant to cut back on work or quit to focus more on their family.

    Cooperative fathers are the next factor. Traditionally, the woman had the majority role in raising children. When the duties of raising children are split more equally, fertility rates can increase as women are better able to balance careers with raising a family.

    Family policies can have an impact on publicly available child care and can ease raising children for fathers and mothers, thereby increasing their ability to raise more children.

    Falling mortality rates can be explained by greater access to nutrition, medicine, and public health. Falling birth rates are due to economic incentives.3

    Falling fertility rates can be correlated with reaching a level of purchasing power. For the last several centuries, fertility rates fell when people obtained purchasing power equal to $2,000 per year in 2011 dollar value. Some theorize that in many countries, this level of purchasing power can be even lower at $1,500.2

    Mortality Definition

    Mortality is being subjected to death, as all living things are.

    Regarding population studies, mortality discusses how many people in a country die each year. When countries are able to develop and grow peacefully, people gain access to better healthcare, and goods and services become more available through large economies with global reach. This allows the quality of life to increase as well as life expectancy, and not as many children are dying before the age of one, lowering the infant mortality rate. If most people live longer, then the mortality rate will be lower. In the demographic transition model, we see that the mortality rate starts decreasing as the main indicator of shifting from stage one to stage two. It can be several decades before fertility rates start to decrease as well.

    In low-income countries, neonatal conditions are the leading cause of death, whereas they are not even in the top 10 in high-income countries. This can be reflected in mortality rates as low-income countries have an infant mortality rate of 47 per 1,000 live births compared with high-income countries have an infant mortality rate of less than a tenth of low-income countries at 4 per 1,000 live births.3

    Other high causes of death in undeveloped, low-income countries that are almost nonexistent in high-income countries are death from diarrheal disease or viruses, mostly due to unsafe drinking water; inadequate sanitation services; and poor hygiene conditions. Malaria is a common cause of death in low-income countries but is relatively preventable or treatable when there is access to healthcare services.4

    Check out our explanations of the Sustainable Development Goals (SDGs)!

    Migration Definition

    Migration can be split into two components: emigration and immigration.

    Emigration is people leaving a country. People will leave a country for many reasons. Some of these reasons might be to search for better work opportunities; conflict; natural disasters; family ties; to make money to send remittances back to their home countries; and a host of others. Usually, less developed countries experience more emigration than developed countries. However, certain factors, such as oppression, corruption, or lack of freedom, can be push factors in more developed countries as well.

    Immigration is people moving to a country. Often the opposite is true here; developed countries experience more immigration than less developed countries because they have more desirable standards of living, quality of life, better access to education, and often, but not always, more freedom, liberty, and less corruption.

    Check out our explanation of the Causes of Migration!

    Immigration can often be a tool for countries to continue economic and population growth when they move into the later stages of the demographic transition model. When a country is developed, the average age typically increases, and the fertility rates decline, which can lead to stagnant economic growth and labor shortages as fewer and fewer people enter the workforce. Immigration can often be an economic boost to a country facing these challenges; however, immigration often comes with shifting and diversified cultural identities that can be met with social resistance.

    The United States had a fertility rate of 1.7 births per woman in 2019.6 This is well below the replacement rate of 2.1 to maintain a consistent population, yet the US population is still growing and projected to grow for the foreseeable future. This is because the United States is the largest destination in the world for migrants. In 2019, it was estimated that close to 51 million people living in the United States were not born there. That’s more than the entire population of countries like Spain, Columbia, or Canada.

    Factors affecting Population Growth, Fertility, Mortality, and Migration

    Factors affecting the demographic makeup of a society can be a country's level of development, health care services, access to goods and services of an industrialized economy, and in the later stages, the balance that people have between career and time to raise a family.

    Fertility, Mortality, and Migration Average Population Change by Country StudySmarterFig. 3 - Average Population Change by Country

    The following table looks deeper at what we can infer from looking at population factors:

    Population DynamicPossible CharacteristicsReal World Example

    High fertility, high mortality, high emigration

    This country is likely very undeveloped or perhaps something of a failed state. There is likely not much industry, and a large portion of the population may still rely on subsistence farming. General health is likely quite low and with little access to healthcare, life expectancy is likely low.

    Chad, Somalia

    High fertility, high mortality, high immigration.

    This country would likely be fairly undeveloped but perhaps neighboring some less desirable countries that may be experiencing conflict or oppression. They may have fairly strong institutions and more protection of rights and liberty than their neighbors. They could be a significant country culturally, perhaps the home of a major religion and therefore might attract people of this faith.


    High fertility, low mortality, high emigration.

    This is a country that has started to move into the second stage of the demographic transition model because the people have reached the quality of life where mortality is starting to drop and economic and demographic booms are beginning. Nonetheless, they may be in close proximity to more desirable countries.

    High fertility, low mortality, and high immigration. This country like is a good place to be in the region; mortality has dropped, life expectancy is getting longer, the economy is growing, and the numbers of youth are very high, presenting a bright economic future. This country is probably also relatively peaceful and may not be ideal but likely has more favorable rights and liberties than many of its neighbors.

    Ivory Coast, Kenya

    Low fertility, high mortality, high emigration

    This is likely a country that is fairly developed but perhaps going through a major crisis, such as a war, or conflict, increasing mortality and driving many people to leave. Alternatively, they are not going through a conflict but have a large aging population and are experiencing economic stagnation as there are more desirable countries to migrate to nearby.

    Ukraine, Bulgaria

    Low fertility, high mortality, high immigration.

    This country may be fairly developed. It may have a large aging population pushing the mortality rate up. It may have some issues with crime, corruption, or inequality; however, it may still have favorable economic opportunities and higher standards of living than the surrounding countries.


    Low fertility, low mortality, high immigration

    This country is highly economically developed. Even though aging populations in these countries can push mortality rates high, quality of life is high and life expectancy is high. The economy is developed but may be slowing. There are ample opportunities that make it a highly desirable country.Australia, USA
    Low fertility, low mortality, high emigration Another developed country with a high quality of life but has some factors that are still pushing people away. Perhaps people do not have many freedom or liberties, inequality of crime may be high, or many people may experience oppression.


    Fertility, Mortality and Migration - Key takeaways

    • Fertility, mortality, and migration are the factors that affect a country's population.
    • Fertility, mortality, and migration can be a lens to explain many a country's current states.
    • Mortality rates decrease before fertility rates.
    • Thus far, when a country develops, the fertility rate drops.


    1. Doepke Matthias, Hannusch Anne, Kindermann Fabian, Tertilt Michele. “The Economics of Fertility.”https://www.imf.org/en/Publications/fandd/issues/2022/analytical-series/new-economics-of-fertility-doepke-hannusch-kindermann-tertilt. September 2022.
    2. The Economist. “Why the demographic transition is speeding up.” https://www.economist.com/finance-and-economics/2021/12/11/why-the-demographic-transition-is-speeding-up. 11, December 2021.
    3. The UN Inter-agnecy Group for Child Mortality Estimation. “Mortality rate, infant (per 1,000 live births).” https://data.worldbank.org/indicator/SP.DYN.IMRT.IN (No Date)
    4. World Health Organization. “The top 10 causes of death.” https://www.who.int/news-room/fact-sheets/detail/the-top-10-causes-of-death .9 December 2020.
    5. Data Commons. “United States of America.” https://datacommons.org/place/country/USA?utm_medium=explore&mprop=fertilityRate&popt=Person&cpv=gender%2CFemale&hl=en. (No Date)
    6. IOM UN Migration. “World Migration Report 2022.” https://worldmigrationreport.iom.int/wmr-2022-interactive/. 2022.
    7. World Population Review. “Low Income Countries 2022.” https://worldpopulationreview.com/country-rankings/low-income-countries 2022.
    8. Freedom House. “Global Freedom Status.” https://freedomhouse.org/explore-the-map?type=fiw&year=2022. 2022.
    9. Our World in Data. “Birth rate vs. death rate, 2021.” https://ourworldindata.org/grapher/birth-rate-vs-death-rate?country=AIA~ATG~ABW~BHS~BRB~BLZ~BMU~BES~VGB~CAN~CYM~CRI~CUB~CUW~DMA~DOM~SLV~GRL~GRD~GLP~GTM~HTI~HND~JAM~MTQ~MEX~MSR~NIC~PAN~PRI~KNA~LCA~MAF~SPM~VCT~SXM~TTO~TCA~USA~VIR. (No Date)
    10. Fig. 1: World Population Projection Pyramid (https://commons.wikimedia.org/wiki/File:Global_Population-Pyramid-1950-to-2100.jpg) by Max Roser (https://www.maxroser.com/) is licensed by CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/deed.en)
    11. Fig. 2: The Demographic Transition Model (https://commons.wikimedia.org/wiki/File:Demographic-TransitionOWID.png) by Max Roser (https://www.maxroser.com/) is licensed by CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/deed.en)
    12. Fig. 3: Average Population Change by Country (https://commons.wikimedia.org/wiki/File:Population-growth-rate-HighRes-2015.png) by Nicxjo (https://commons.wikimedia.org/wiki/User:Nicxjo) is licensed by CC BY 3.0 (https://creativecommons.org/licenses/by/3.0/deed.en)
    Frequently Asked Questions about Fertility, Mortality and Migration

    What factors influence fertility, mortality, and migration rates?

    Predominantly the level of economic development, along with factors such as conflict, liberties, and opportunities.

    What are fertility and mortality?

    Fertility refers to the number of people born in a population, whereas mortality refers to the number of deaths.

    How does migration affect fertility?

    Migration can often compensate for low fertility levels to keep populations growing. 

    How do fertility and mortality rates affect population growth?

    If fertility is higher than mortality, the population is growing. If mortality is higher than fertility, then the population is getting smaller. 

    What is the study of the population processes of fertility, mortality, and migration?

    It is the study of demographics and changes in populations. Fertility, mortality, and migration are all factors that change the makeup of a population.

    Test your knowledge with multiple choice flashcards

    If a country has a low fertility rate, low mortality rate, and a lot of immigration, what might you be able to infer about the country?

    If fertility and mortality are the same but a country has more immigration than emigration, what is happening to the population?

    If a country has a high fertility rate, low mortality rate, and a lot of emigration, what might you be able to infer about the country?


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