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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<span class="mw-page-title-main">Demography</span> Science that deals with populations and their structures, statistically and theoretically

Demography is the statistical study of human populations: their size, composition, and how they change through the interplay of fertility (births), mortality (deaths), and migration.

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In demography, demographic transition is a phenomenon and theory which refers to the historical shift from high birth rates and high death rates to low birth rates and low death rates, as societies attain more technology, education and economic development. The demographic transition has occurred in most of the world over the past two centuries, bringing the unprecedented population growth of the post-Malthusian period, then reducing birth rates and population growth significantly in all regions of the world. The demographic transition strengthens economic growth process by three changes: (i) reduced dilution of capital and land stock, (ii) increased investment in human capital, and (iii) increased size of the labor force relative to the total population and changed age population distribution. 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.

<span class="mw-page-title-main">Birth rate</span> Total number of live births per 1,000 divided by time period

Birth rate, also known as natality, is the total number of live human births per 1,000 population for a given period 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.

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<span class="mw-page-title-main">Total fertility rate</span> 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 are born to a woman over her lifetime, if they were to experience the exact current age-specific fertility rates (ASFRs) through their lifetime, and they were to live from birth until the end of their reproductive life.

<span class="mw-page-title-main">Sub-replacement fertility</span> 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 global average fertility rate was around 2.4 children born per woman.

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<span class="mw-page-title-main">Population pyramid</span> 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.

<span class="mw-page-title-main">Epidemiological transition</span> A term in demography

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<span class="mw-page-title-main">Rate of natural increase</span>

In demography and population dynamics, 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.

<span class="mw-page-title-main">Ageing of Europe</span> 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.

<span class="mw-page-title-main">Demographics of the world</span> Global human population statistics

Earth has a human population of over 8 billion as of 2024, with an overall population density of 50 people per km2. Nearly 60% of the world's population lives in Asia, with more than 2.8 billion in the countries of India and China combined. The percentage shares of China, India and rest of South Asia of the world population have remained at similar levels for the last few thousand years of recorded history. The world's literacy rate has increased dramatically in the last 40 years, from 66.7% in 1979 to 86.3% today. Lower literacy levels are mostly attributable to poverty. Lower literacy rates are found mostly in South Asia and Sub-Saharan Africa.

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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