The Demographic Transition is name given to the process that has occurred during the past century, leading to a stabilization of population growth in the more highly developed countries. It is generally characterized as having four separate phases or stages.
Stage 1: In this early stage of the demographic transition, birth rates and death rates are both high. Modern medicine had not yet developed techniques to lengthen life substantially and standards of personal hygiene were comparatively low. Both rates fluctuated depending on circumstances. Countries in these stages have a very low life expectancy. Examples of countries currently classified as Stage 1 includes Niger and Uganda.
Stage 2. In this stage, standards of hygiene and more modern medical techniques began to drive the death rate down, leading to a significant upward trend in population size (population growth). The birth rate remained high, as much of the economy was based on agriculture. There is slightly longer life expectancy and the fall in death rate has resulted in more people living into a middle age. Haiti is currently between this and the following stage. Stage 2 and 3 are indicative of a partial or first demographic transition.
There are several causes for high birth rates in stages 1 and 2 of the DTM (Demographic Transition Model). They include the need for children for farming or income, high infant mortality rates, societal and religious values and in some cases in lack of family planning information / technology.
Stage 3. Evidence of urbanisation decreases the economic incentives for large families. The cost of supporting an urban family grew and parents were more actively discouraged from having large families. In response to these economic pressures, the birth rate started to drop, ultimately coming close to the death rate. This stage is associated with stable population growth as birth rates decline and life expectancy increases. A increasing proportion of the population is reaching the over 65 age group. In this stage, infant mortality rates also drop due to access to health care, education and nutrition. Examples of countries in this stage include Morocco and Mexico.
The last stage of the demographic transition is characterized by a higher, but stable, population size. Birth and death rates were both relatively low and the standard of living became much higher than during the earlier periods. The developed world remains in the fourth stage of its demographic transition.
As birth rates and death rates continue to decline, population growth will eventually decline. This stage also shows the presence of a high dependency ratio.
Examples of countries in this stage include, Argentina, Australia and Sweden
Stage 5 of the DTM a country experiences loss to the overall population as the death rate becomes higher than the birth rate. The negative population growth rate is not an immediate effect however. Based on demographic momentum, in which total population growth increases even while birth rates decline, it will take a generation or two before a negative population growth rate is observed.
In this scenario it is the economy that is the driving force behind further limits on family size and the use of contraception. Whether persuaded by the high costs of raising a family in cities or the enticing opportunities of employment that delay child bearing, birth rates decline well below replacement level (2.1 children per woman). What occurs is an aging citizenry that will eventually lead to a decrease in total population.
Examples include: Germany, Singapore, Japan and Croatia.