Reasons for different types of population structures as shown by age/sex pyramids

There are 4 types of population structures or pyramids:


  • Stationary/Stable Pyramid: This pyramid shows low fertility and mortality rates that remain balanced or unchanged.
  • Expansive Pyramid: This pyramid is wide at its base, indicative of high birth and death rates.
  • Constrictive Pyramid: Indicating low birth and death rates, this pyramid has a constricted base. This pattern is typical of developed countries where literacy rates are high and the life- expectancy of individuals is long.
  • Declining Pyramid: Indicative of low birth rates and long life – expectancies, this pyramid has a diminishing base.

Reasons for different population structures:

According to the DTM (Demographic Transition Model) the population growth of countries around the world go through 5 distinct stages.

1st stage:

Certain Sub – Saharan and Middle Eastern countries are currently going through the first stage. Though their societies and economies are under – developed the birth and death rates in these regions are high and relatively equal or balanced. Population growth is slow due to lack of progress in the fields of science, technology and healthcare. The Literacy rate and average life – expectancy is low too. Unsanitary living conditions, lack of proper infrastructure and insufficient awareness about contraception keeps birth and death rates high. Countries going through this stage show expansive characteristics. The population structure in these countries is depicted by a high – fluctuating pyramid that’s similar to an expansive pyramid but has a concave profile.

2nd stage:

Developing countries like India, Pakistan, Mexico, Turkey etc. are going through the 2nd stage. This stage is characterised by high birth rates and low death rates due to improvements made in the fields of technology and medicine. The living conditions in these nations are relatively hygienic and literacy rates are on the rise. Advanced in agricultural techniques and an abundance of food helps support growing populations and increases the average life – expectancy of individuals. Countries going through this stage experience a lot of growth in population. The population in these countries are characterised by an expansive pyramid.

3rd stage:

Majority of the countries which have achieved stage three status are developing countries in transition. Due to rapid progress in these regions (developing countries) they seem to be between the 2nd and 3rd stage. These nations have low birth rates due to high rates of literacy and increased awareness regarding contraception. Literacy or education plays an important role in controlling birth rates because individuals study about the adverse effects of overpopulation and the spread of STD’s (Sexually transmitted diseases) at educational institutions which inevitably limits or deters population growth. Urbanisation and education is prioritised. Population expansion or growth begins to even out. The population structure in these regions is relatively stable or stationary. Stationary pyramids have a convex profile with a wide base.

4th stage:

Most developed countries like USA, UK and France fall under this category. These nations have low and stable birth and death rates. Birth rates are low in this region due to high rates of literacy and the availability of contraception. The average life – expectancy of individuals in these regions is high due to the abundance of food and healthcare. The population structure in these countries is characterised by a constrictive pyramid.

5th stage:

Countries like Greece, Germany and Ukraine are currently going through the fifth stage of the Demographic Transition Model where there’s a decline in the population due to low birth rates and long life – expectancies. The population structure of these nations is depicted by a pyramid that has a convex profile and a diminishing base.

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