Population change

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Population change is simply the change in the number of people in a specified area during a specific time period. Demographics (or demography) is the study of population statistics, their variation and its causes. These statistics include birth rates, death rates (and hence life expectancy), migration rates and sex ratios. All of these statistics are investigated by censuses and surveys conducted over a period of time. [1] Some demographic information can also be obtained from historical maps, and aerial photographs. [2]

A major purpose of demography is to inform government and business planning of the resources that will be required as a result of population changes. [3]

The change in total population over a period is equal to the number of births, minus the number of deaths, plus or minus the net amount of migration in a population. The number of births can be projected as the number of females at each relevant age multiplied by the assumed fertility rate. The number of deaths can be projected as the sum of the numbers of each age and sex in the population multiplied by their respective mortality rates. For many centuries, the overall population of the world changed relatively slowly: very broadly, the numbers of births were balanced by numbers of deaths (including high rates of infant immortality). Infant mortality was high for various reasons such as ignorance, insufficient health facilities, and sometimes lack of food. Occasionally, farmers were unable to produce enough food for the population, resulting in death from starvation. However more recently, and especially in the 20th and 21st centuries, due to growth in technology, education, and medical care, the world population has increased rapidly, as many more people have survived to child-bearing age. Natural resources that were once scarce are now being mass-produced. Because of this increase, some countries have adopted policies to try to control population growth. These policies include active measures to reduce the numbers of births (e.g. "one-child policy") as well as education. [4] In many countries, fertility rates have declined, due to better education, better available birth control, better pension provision reducing economic dependence on one's children in old age, and in response to lower infant mortality. Those who wait until they are older before starting a family may find it more difficult to do so as fertility declines with age. One of the biological reasons for this is abnormal chromosome segregation during cell division in older eggs. [5] In some parts of society there are also now more women formally employed in the workforce. Recent studies show that there has been a decline in fertility from the ages 25 to 29. [6] In general, fertility rates have relatively decreased at ages under 30. [6]

One way to visualize population change is to examine population pyramids. These display graphically how many people of each gender there are in each age bracket in a given population. [7] (A pyramid with a wider base and a smaller top, thus a triangle shape, shows rapid population growth, while a more rectangular shape shows a more stable population.) [8] Many countries have differently-shaped population pyramids, due to the factors discussed above, mainly historically different birth and death rates, and in some cases forced changes in population such as war, ethnic cleansing and genocide. Examples of population pyramids by year can be found here.

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Demographic transition Significant changes in birth and death rates

In demography, demographic transition is a phenomenon and theory which refers to the historical shift from high birth rates and high death rates in societies with minimal technology, education and economic development, to low birth rates and low death rates in societies with advanced technology, education and economic development, as well as the stages between these two scenarios. Although this shift has occurred in many industrialized countries, the theory and model are frequently imprecise when applied to individual countries due to specific social, political and economic factors affecting particular populations.

A baby boom is a period marked by a significant increase of birth rate. This demographic phenomenon is usually ascribed within certain geographical bounds of defined national and cultural populations. People born during these periods are often called baby boomers. The cause of baby booms involves various fertility factors. The best-known baby boom occurred in the mid-twentieth century, sometimes considered to have started after the end of the Second World War, sometimes from the late 1930s, and ending in the 1960s.

Birth rate Total number of live births per 1,000 population divided by the length of a given period in years

The birth rate for a given period is the total number of live human births per 1,000 population divided by the length of the period in years. The number of live births is normally taken from a universal registration system for births; population counts from a census, and estimation through specialized demographic techniques. The birth rate is used to calculate population growth. The estimated average population may be taken as the mid-year population.

Zero population growth, sometimes abbreviated ZPG, is a condition of demographic balance where the number of people in a specified population neither grows nor declines, that is, the number of births plus in-migrants equals the number of deaths plus out-migrants. ZPG has been a prominent political movement since the 1960’s. As part of the concept of optimum population, the movement considers zero population growth to be an objective towards which countries and the whole world should strive in the interests of accomplishing long-term optimal standards and conditions of living.

Total fertility rate Number of children a woman is expected to have barring select circumstances

The total fertility rate (TFR) of a population is the average number of children that would be born to a woman over her lifetime if:

  1. she were to experience the exact current age-specific fertility rates (ASFRs) through her lifetime
  2. she were to live from birth until the end of her reproductive life.
Sub-replacement fertility Total fertility rate that (if sustained) leads to each new generation being less populous

Sub-replacement fertility is a total fertility rate (TFR) that leads to each new generation being less populous than the older, previous one in a given area. The United Nations Population Division defines sub-replacement fertility as any rate below approximately 2.1 children born per woman of childbearing age, but the threshold can be as high as 3.4 in some developing countries because of higher mortality rates. Taken globally, the total fertility rate at replacement was 2.33 children per woman in 2003. This can be "translated" as 2 children per woman to replace the parents, plus a "third of a child" to make up for the higher probability of males born and mortality prior to the end of a person's fertile life. In 2020, the average global fertility rate was around 2.4 children born per woman.

A population decline in humans is a reduction in a human population size. Over the long term, stretching from prehistory to the present, Earth's total human population has continued to grow; however, current projections suggest that this long-term trend of steady population growth may be coming to an end.

Population growth Increase in the number of individuals in a population

Population growth is the increase in the number of people in a population or dispersed group. Global human population growth amounts to around 83 million annually, or 1.1% per year. The global population has grown from 1 billion in 1800 to 7.9 billion in 2020. The UN projected population to keep growing, and estimates have put the total population at 8.6 billion by mid-2030, 9.8 billion by mid-2050 and 11.2 billion by 2100. However, some academics outside the UN have increasingly developed human population models that account for additional downward pressures on population growth; in such a scenario population would peak before 2100.

Population pyramid Graphical illustration showing distribution of age groups in a population

A population pyramid or "age-sex pyramid" is a graphical illustration of the distribution of a population by age groups and sex; it typically takes the shape of a pyramid when the population is growing. Males are usually shown on the left and females on the right, and they may be measured in absolute numbers or as a percentage of the total population. The pyramid can be used to visualize the age of a particular population. It is also used in ecology to determine the overall age distribution of a population; an indication of the reproductive capabilities and likelihood of the continuation of a species. Number of people per unit area of land is called population density.

Epidemiological transition

In demography and medical geography, epidemiological transition is a theory which "describes changing population patterns in terms of fertility, life expectancy, mortality, and leading causes of death." For example, a phase of development marked by a sudden increase in population growth rates brought by improved food security and innovations in public health and medicine, can be followed by a re-leveling of population growth due to subsequent declines in fertility rates. Such a transition can account for the replacement of infectious diseases by chronic diseases over time due to increased life span as a result of improved health care and disease prevention. This theory was originally posited by Abdel Omran in 1971.

Rate of natural increase

In Demography, the rate of natural increase (RNI), also known as natural population change, is defined as the birth rate minus the death rate of a particular population, over a particular time period. It is typically expressed either as a number per 1,000 individuals in the population or as a percentage. RNI can be either positive or negative. It contrasts to total population change by ignoring net migration.

Ageing of Europe Overview of ageing in Europe

The ageing of Europe, also known as the greying of Europe, is a demographic phenomenon in Europe characterised by a decrease in fertility, a decrease in mortality rate, and a higher life expectancy among European populations. Low birth rates and higher life expectancy contribute to the transformation of Europe's population pyramid shape. The most significant change is the transition towards a much older population structure, resulting in a decrease in the proportion of the working age while the number of the retired population increases. The total number of the older population is projected to increase greatly within the coming decades, with rising proportions of the post-war baby-boom generations reaching retirement. This will cause a high burden on the working age population as they provide for the increasing number of the older population.

Demographic analysis examines and measures the dimensions and dynamics of populations. These methods have primarily been developed to study human populations, but are extended to a variety of areas where researchers want to know how populations of social actors can change across time through processes of birth, death, and migration. In the context of human biological populations, demographic analysis uses administrative records to develop an independent estimate of the population. Demographic analysis estimates are often considered a reliable standard for judging the accuracy of the census information gathered at any time. In the labor force, demographic analysis is used to estimate sizes and flows of populations of workers; in population ecology the focus is on the birth, death, migration and immigration of individuals in a population of living organisms, alternatively, in social human sciences could involve movement of firms and institutional forms. Demographic analysis is used in a wide variety of contexts. For example, it is often used in business plans, to describe the population connected to the geographic location of the business. Demographic analysis is usually abbreviated as DA. For the 2010 U.S. Census, The U.S. Census Bureau has expanded its DA categories. Also as part of the 2010 U.S. Census, DA now also includes comparative analysis between independent housing estimates, and census address lists at different key time points.

References

  1. ↑ Population Reference Bureau's Population Handbook (Sixth Edition). Twelfth printing. 2011. pp. 2–33. ISBN   0-917136-12-8.
  2. ↑ "This fascinating time-lapse show how New York City's population density changed over 210 years". Business Insider. Retrieved 2017-04-05.
  3. ↑ "Sustainability megatrends: The ever-changing landscape of population growth and social change". edie.net. Retrieved 2017-04-05.
  4. ↑ Bongaarts, John (2016). Slow Down Population Growth. Macmillan Publisher Limited.
  5. ↑ "Why Fertility Declines in Some Women as They age". LabRoots. Retrieved 2017-04-05.
  6. 1 2 Howe, Neil. "U.S. Fertility: Down For The Count". Forbes. Retrieved 2017-04-05.
  7. ↑ "The world reshaped". The Economist. 2014-11-20. ISSN   0013-0613 . Retrieved 2017-04-05.
  8. ↑ TED-Ed (2014-05-05), Population pyramids: Powerful predictors of the future - Kim Preshoff, archived from the original on 2021-12-21, retrieved 2017-04-05
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