Demographic transition


Diagram which includes stage five

The Demographic transition model (DTM) is a model used to represent the process of explaining the transformation of countries from high birth rates and high death rates to low birth rates and low death rates as part of the economic development of a country from a pre-industrial to an industrialized economy. It is based on an interpretation begun in 1929 by the American demographer Warren Thompson [1] of prior observed changes, or transitions, in birth and death rates in industrialized societies over the past two hundred years.

Most developed countries are beyond stage three of the model; the majority of developing countries are in stage 2 or stage 3. The model was based on the changes seen in Europe so these countries follow the DTM relatively well. Many developing countries have moved into stage 3. The major (relative) exceptions are some poor countries, mainly in sub-Saharan Africa and some Middle Eastern countries, which are poor or affected by government policy or civil strife, notably Pakistan, Palestinian Territories, Yemen and Afghanistan.[2]

Note that this model predicts ever decreasing fertility rates, whereas recent data shows that after a certain level of development the fertility increases again [3].

Contents

Summary of the theory

Population pyramids for 4 stages of the model
Demographic change in Sweden from 1735 to 2000.
Red line: crude death rate (CDR), blue line: (crude) birth rate (CBR)

The transition involves four stages, or possibly five.

  • In stage one, pre-industrial society, death rates and birth rates are high and roughly in balance.
  • In stage two, that of a developing country, the death rates drop rapidly due to improvements in food supply and sanitation, which increase life spans and reduce disease. These changes usually come about due to improvements in farming techniques, access to technology, basic healthcare, and education. Without a corresponding fall in birth rates this produces an imbalance, and the countries in this stage experience a large increase in population.
  • In stage three, birth rates fall due to access to contraception, increases in wages, urbanization, a reduction in subsistence agriculture, an increase in the status and education of women, a reduction in the value of children's work, an increase in parental investment in the education of children and other social changes. Population growth begins to level off.
  • During stage four there are both low birth rates and low death rates. Birth rates may drop to well below replacement level as has happened in countries like Germany, Italy, and Japan, leading to a shrinking population, a threat to many industries that rely on population growth. As the large group born during stage two ages, it creates an economic burden on the shrinking working population. Death rates may remain consistently low or increase slightly due to increases in lifestyle diseases due to low exercise levels and high obesity and an aging population in developed countries.

As with all models, this is an idealized picture of population change in these countries. The model is a generalization that applies to these countries as a group and may not accurately describe all individual cases. The extent to which it applies to less-developed societies today remains to be seen. Many countries such as China, Brazil and Thailand have passed through the DTM very quickly due to fast social and economic change. Some countries, particularly African countries, appear to be stalled in the second stage due to stagnant development and the effect of AIDS.

Stage One

In pre-industrial society, death rates and birth rates were both high and fluctuated rapidly according to natural events, such as drought and disease, to produce a relatively constant and young population. Children contributed to the economy of the household from an early age by carrying water, firewood, and messages, caring for younger siblings, sweeping, washing dishes, preparing food, and working in the fields.[4]

Raising a child cost little more than feeding him; there were no education or entertainment expenses and, in equatorial Africa, there were no clothing expenses either. Thus, the total cost of raising children barely exceeded their contribution to the household. In addition, as they became adults they become a major input to the family business, mainly farming, and were the primary form of insurance for adults in old age. In India, an adult son was all that prevented a widow from falling into destitution. While death rates remained high there was no question as to the need for children, even if the means to prevent them had existed.[5]

Stage Two

World population 10,000 BC - 2000 AD

This stage leads to a fall in death rates and an increase in population.[6] The changes leading to this stage in Europe were initiated in the Agricultural Revolution of the 18th century and were initially quite slow. In the 20th century, the falls in death rates in developing countries tended to be substantially faster. Countries in this stage include Yemen, Afghanistan, the Palestinian territories, Bhutan and Laos and much of Sub-Saharan Africa (but do not include South Africa, Zimbabwe, Botswana, Swaziland, Lesotho, Namibia, Kenya and Ghana, which have begun to move into stage 3).[7]

The decline in the death rate is due initially to two factors:

  • First, improvements in the food supply brought about by higher yields in agricultural practices and better transportation prevent death due to starvation and lack of water. Agricultural improvements included crop rotation, selective breeding, and seed drill technology.
  • Second, significant improvements in public health reduce mortality, particularly in childhood. These are not so much medical breakthroughs (Europe passed through stage two before the advances of the mid-20th century, although there was significant medical progress in the 19th century, such as the development of vaccination) as they are improvements in water supply, sewerage, food handling, and general personal hygiene following from growing scientific knowledge of the causes of disease and the improved education and social status of mothers.

A consequence of the decline in mortality in Stage Two is an increasingly rapid rise in population growth (a "population explosion") as the gap between deaths and births grows wider. Note that this growth is not due to an increase in fertility (or birth rates) but to a decline in deaths. This change in population occurred in northwestern Europe during the 19th century due to the Industrial Revolution. During the second half of the 20th century less-developed countries entered Stage Two, creating the worldwide population explosion that has demographers concerned today.

Angola 2005

Another characteristic of Stage Two of the demographic transition is a change in the age structure of the population. In Stage One, the majority of deaths are concentrated in the first 5–10 years of life. Therefore, more than anything else, the decline in death rates in Stage Two entails the increasing survival of children and a growing population. Hence, the age structure of the population becomes increasingly youthful and more of these children enter the reproductive cycle of their lives while maintaining the high fertility rates of their parents. The bottom of the "age pyramid" widens first, accelerating population growth. The age structure of such a population is illustrated by using an example from the Third World today.

Stage Three

Stage Three moves the population towards stability through a decline in the birth rate.[8] There are several factors contributing to this eventual decline, although some of them remain speculative:

  • In rural areas continued decline in childhood death means that at some point parents realize they need not require so many children to be born to ensure a comfortable old age. As childhood death continues to fall and incomes increase parents can become increasingly confident that fewer children will suffice to help in family business and care for them in old age.
  • Increasing urbanization changes the traditional values placed upon fertility and the value of children in rural society. Urban living also raises the cost of dependent children to a family. A recent theory suggests that urbanization also contributes to reducing the birth rate because it disrupts optimal mating patterns. A 2008 study in Iceland found that the most fecund marriages are between distant cousins. Genetic incompatibilities inherent in more distant outbreeding makes reproduction harder.[9]
  • In both rural and urban areas, the cost of children to parents is exacerbated by the introduction of compulsory education acts and the increased need to educate children so they can take up a respected position in society. Children are increasingly prohibited under law from working outside the household and make an increasingly limited contribution to the household, as school children are increasingly exempted from the expectation of making a significant contribution to domestic work. Even in equatorial Africa, children now need to be clothed, and may even require school uniforms. Parents begin to consider it a duty to buy children books and toys. Partly due to education and access to family planning, people begin to reassess their need for children and their ability to raise them.[5]
    A major factor in reducing birth rates in stage 3 countries such as Malaysia is the availability of family planning facilities, like this one in Kuala Terenganu, Terenganu, Malaysia.
  • Increasing female literacy and employment lower the uncritical acceptance of childbearing and motherhood as measures of the status of women. Working women have less time to raise children; this is particularly an issue where fathers traditionally make little or no contribution to child-raising, such as southern Europe or Japan. Valuation of women beyond childbearing and motherhood becomes important.
  • Improvements in contraceptive technology are now a major factor. Fertility decline is caused as much by changes in values about children and sex as by the availability of contraceptives and knowledge of how to use them.

The resulting changes in the age structure of the population include a reduction in the youth dependency ratio and eventually population aging. The population structure becomes less triangular and more like an elongated balloon. During the period between the decline in youth dependency and rise in old age dependency there is a demographic window of opportunity that can potentially produce economic growth through an increase in the ratio of working age to dependent population; the demographic dividend.

However, unless factors such as those listed above are allowed to work, a society's birth rates may not drop to a low level in due time, which means that the society cannot proceed to Stage Four and is locked in what is called a demographic trap.

Countries that have experienced a fertility decline of over 40% from their pre-transition levels include: Costa Rica, El Salvador, Panama, Jamaica, Mexico, Colombia, Ecuador, Guyana, Surinam, Philippines, Indonesia, Malaysia, Sri Lanka, Turkey, Azerbaijan, Turkmenistan, Uzbekistan, Egypt, Tunisia, Algeria, Morocco, Lebanon, South Africa, India, Saudi Arabia, and many Pacific islands.

Countries that have experienced a fertility decline of 25-40% include: Honduras, Guatemala, Nicaragua, Paraguay, Bolivia, Vietnam, Myanmar, Bangladesh, Tajikistan, Jordan, Qatar, Albania, United Arab Emirates, Zimbabwe, and Botswana.

Countries that have experienced a fertility decline of 10-25% include: Haiti, Papua New Guinea, Nepal, Pakistan, Syria, Iraq, Libya, Sudan, Kenya, Ghana and Senegal.[7]

Stage Four

This occurs where birth and death rates are both low. Therefore the total population is high and stable.[10] Some theorists consider there are only 4 stages and that the population of a country will remain at this level. The DTM is only a suggestion about the future population levels of a country. It is not a prediction.

Countries that are at this stage (Total Fertility Rate of less than 2.5 in 1997) include: United States, Canada, Argentina, Australia, New Zealand, most of Europe, Bahamas, Puerto Rico, Trinidad and Tobago, Brazil, Sri Lanka, South Korea, Singapore, Iran, China, Turkey, North Korea, Thailand and Mauritius.[7]

Stage Five

See also: Aging of Europe and Aging of Japan
United Nation's population projections by location.
Note the vertical axis is logarithmic & is millions of people.

The original Demographic Transition model has just four stages; however, some theorists consider that a fifth stage is needed to represent countries that have sub-replacement fertility. Most European and many East Asian countries now have higher death rates than birth rates.

There may be a further stage of demographic development. In an article in the August 2009 issue of Nature, Myrskyla, Kohler and Billari show that previously negative relationship between national wealth (as measured by the human development index (HDI) and birth rates has become J-shaped. Development promotes fertility decline at low and medium HDI levels, but advanced HDI promotes a rebound in fertility.[11] In many countries with very high levels of development (around 0.95) fertility rates are now approaching two children per woman - although there are exceptions, notably Canada and Japan.[12]

Effects on age structure

The decline in death rate and birth rate that occurs during the demographic transition leads to a radical transformation of the age structure. When the death rate declines during the second stage of the transition, the result is primarily an increase in the child population. The reason is that when the death rate is high (stage one), the infant mortality rate is very high, often above 200 deaths per 1000 children born. When the death rate falls or improves, this, in general, results in a significantly lower infant mortality rate and, hence, increased child survival. Over time, as cohorts increased by higher survival rates get older, there will also be an increase in the number of older children, teenagers, and young adults. This implies that there is an increase in the fertile population which, with constant fertility rates, will lead to an increase in the number of children born. This will further increase the growth of the child population. The second stage of the demographic transition, therefore, implies a rise in child dependency.

Critical evaluation

It has to be remembered that the DTM is only a model and cannot necessarily predict the future. It does however give an indication of what the future birth and death rates may be for an underdeveloped country, together with the total population size. Most particularly, of course, the DTM makes no comment on change in population due to migration. It is not applicable for high levels of development, as it has been shown that after a HDI of 0.9 the fertility increases again [13].

Non-applicability to less-developed countries

DTM has a questionable applicability to less economically developed countries (LEDCs), where wealth and information access are limited. For example, the DTM has been validated primarily in Europe, Japan and North America where demographic data exists over centuries, whereas high quality demographic data for most LDCs did not become widely available until the mid 20th century.[14] DTM does not account for recent phenomena such as AIDS; in these areas HIV has become the leading source of mortality. Some trends in waterborne bacterial infant mortality are also disturbing in countries like Malawi, Sudan and Nigeria; for example, progress in the DTM clearly arrested and reversed between 1975 and 2005.[15]

Economic development not sufficient cause to effect demographic change

DTM assumes that population changes are induced by industrial changes and increased wealth, without taking into account the role of social change in determining birth rates, e.g., the education of women. In recent decades more work has been done on developing the social mechanisms behind it.[2]

DTM assumes that the birth rate is independent of the death rate. Nevertheless, demographers maintain that there is no historical evidence for society-wide fertility rates rising significantly after high mortality events. Notably, some historic populations have taken many years to replace lives such as the Black Death.

Some have claimed that DTM does not explain the early fertility declines in much of Asia in the second half of the 20th century or the delays in fertility decline in parts of the Middle East. Nevertheless, the demographer John C Caldwell has suggested that the reason for the rapid decline in fertility in some developing countries compared to Western Europe, the United States, Canada, Australia and New Zealand is mainly due to government programs and a massive investment in education both by governments and parents.[7]

Application to the U.S. in the 19th and 20th centuries

A simplification of the DTM theory proposes an initial decline in mortality followed by a later drop in fertility. The changing demographics of the U.S. in the last two centuries did not parallel this model. Beginning around 1800, there was a sharp fertility decline; at this time, an average woman usually produced seven births per lifetime, but by 1900 this number had dropped to nearly four. A mortality decline was not observed in the U.S. until almost 1900—a hundred years following the drop in fertility.

However, this late decline occurred from a very low initial level. It's been estimated that the crude death rate in 17th century rural New England was already as low as 20 deaths per 1000 residents per year (levels of up to 40 per 1000 being typical during stages one and two). The phenomenon is explained by the pattern of colonization of the United States: high death rates unavoidably had to match high birth rates in densely populated Europe, whereas, in the United States, westward expansion of the frontier into sparsely populated interior allowed ample room to absorb all the excess people, resulting in exponential population growth (from less than 4 million people in 1790, to 23 million in 1850, to 76 million in 1900.)

Today, the U.S. is recognized as having both low fertility and mortality rates. Specifically, birth rates stand at 14 per 1000 per year and death rates at 8 per 1000 per year.[16]

See also

Further reading

References

  1. ^ "Warren Thompson". Encyclopedia of Population. 2. Macmillan Reference. 2003. pp. 939–940. ISBN 0-02-865677-6. 
  2. ^ a b Caldwell, John C.; Bruce K Caldwell, Pat Caldwell, Peter F McDonald, Thomas Schindlmayr (2006). Demographic Transition Theory. Dordrecht, The Netherlands: Springer. pp. 418. ISBN 1-4020-4373-2. ,p239
  3. ^ "Advances in development reverse fertility declines". Nature. 6 August 2009. http://www.nature.com/nature/journal/v460/n7256/abs/nature08230.html. 
  4. ^ Barcelona fieldwork
  5. ^ a b Caldwell (2006), Chapter 5
  6. ^ BBC bitesize
  7. ^ a b c d Caldwell (2006), Chapter 10
  8. ^ Marathon geography
  9. ^ "Kissing cousins, missing children". The Economist 7 February 2008.
  10. ^ Main vision
  11. ^ Myrskyla, M., Kohler, H-P., and Billari, F. Advances in development reverse fertility declines. Nature 460, 741-743 (6 August 2009).
  12. ^ "The best of all possible worlds?" The Economist 6 August 2009.
  13. ^ "Advances in development reverse fertility declines". Nature. 6 August 2009. http://www.nature.com/nature/journal/v460/n7256/abs/nature08230.html. 
  14. ^ Ronald Lee, The Demographic Transition: Three Centuries (2003)
  15. ^ Nigeria: Reversal of Demographic Transition
  16. ^ World factbook
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