- In stage one, pre-industrial society, death rates and birth rates are high.
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In stage two, 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. There is a large increase in .
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In stage three, birth rates fall due to access to , increases in wages, , a reduction in , 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.
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During stage four there are both low birth rates and low death rates. 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 and an aging population in .
This pattern has been the case for many developed countries but in some countries however war, disease, cultural reasons and migration have either reversed, caused a stage to be skipped or made a country enter an unpredicted stage.
For instance in Botswana, an LEDC, the country appears to be going backwoods rather than forwards this is due to does ; fully 94 percent of all HIV cases are found in underdeveloped countries, therefore mortality has increased the mortality rates. Some trends in waterborne bacterial infant mortality are also disturbing in countries like , and ; for example, progress in the DTM model clearly arrested and reversed between 1975 and 2005. Another LEDC, Afghanistan isn’t moving out of stage two for cultural and political reasons, the DTM doesn’t take these reasons into account as it believes a country’s population will rise and fall due to death and birth rates.
Some countries may even skip stages or go through a stage a lot quicker than a MEDC as imports from the west allow countries to industrialize a lot faster, transnational corporations move to LEDC’s bringing industrialization a lot quicker than would be expected from looking at the DTM.
In MEDC’s, such as the UK, migration has had a huge impact on birth rates, this makes birth rates rise, the demographic transition model does not take migration into consideration as stage 4 predicts that birth and death rates remain low, fluctuating to give a steady population however due to migration the UK’s population is rising. The DTM also only allowed for 4 stages however some European countries such as Germany have entered what is known as stage 5, in this stage birth rate has fallen below replacement level allowing population to decrease. This again is not predicted by the DTM.