PD - How is Population Studied? (Lesson)
How is Population Studied?
Imagine for a moment 3 groups of countries, each with a different population pyramid. The first has a huge bulge at the bottom, the second is wider in the middle and the third is relatively broad at the top.
If this represents the world in 2025, what can we expect?
The Congressional Budget Office (CBO) report tells some of the story:
3 Groups:
We can start by dividing the world into developed, developing, and underdeveloped nations.
- The more developed countries of the world would include most of Western and Eastern Europe, New Zealand, Canada, and Japan.
- In the middle group, commonly called the developing countries, we could list many Latin American countries like Brazil and Argentina. Kenya is an example in Africa. For Asia, there is India, and in the Pacific, Indonesia.
- For the underdeveloped countries, we would identify Ethiopia, Uganda, many other African nations, and Haiti and Samoa are examples. (In the CBO report, the U.S. and China were presented separately.)
4 Demographic Stages:
Historically, due to disease and limitations on food production, the human population would be subject to high birth rates and high death rates. A woman may have 10 children in her lifetime and only a few would have reached maturity to have his or her own children. Over time, these two rates balanced each other out and the human population remained steady.
World Population to Present Day
In recent years, medicine and other technological advances have decreased the death rate and increased food production. This has led to an overall increase in the population of the world. As individual populations move from underdeveloped to developed, they will undergo 3 distinct changes after centuries of high mortality and fertility rates.
- Stage 1 - Initially there are high birth rates and high death rates which "cancel" each other out. Overall population, shown in black, remains low and steady
- Stage 2 - Due to advances in health care, the development of modern technology, and better sanitation, birth rates remain high, but more children live. The death rate decreases as fewer people die due to illness and the overall length of life increases. The result is an increase in population. Depending on the characteristics of the initial population, this growth rate can be quite high.
- Stage 3 - When these children grow up and become young adults, they tend to have fewer children than the previous generation. The birth rate will begin to decline and population growth will slow.
- Stage 4 - Birth Rates and death rates have once again become harmonious, this time at the low end of the spectrum. Death rates "cancel" birth rates and the total population will steady. Depending on the population, birth rates may even become lower than death rates, leading to a declining population.
3 Population Pyramids
Each of the stages described above can also be seen in population pyramids.
In stage 1, the population bulge is at the bottom of the pyramid, stage 2, in the bottom and middle, and stage 3 and 4 at the top.
Balanced
A balanced age structure generally has the same number of individuals throughout each age group and represents a stable population and no growth. Examples include Denmark, Austria, and Spain.
Pyramid Shape
A pyramid-shaped diagram reflects a population with a large number of young people. This is a growing population, and in the long term, this population will increase assuming no major changes to any particular group. A pyramid can represent either rapid growth or slow growth. Examples of rapid growth (a steep-sided pyramid) include Afghanistan, Angola, Kenya, Nigeria, and Guatemala. Examples of slow growth (gently sloping pyramid) include the USA and Canada.
Inverted Pyramid
An inverted pyramid structure, or diamond-shaped structure, shows an aging population with fewer young. This population will decline over time, but it may put pressure on the young to take care of the elderly. Also, there could be a decline in the economy and in the strength of that nation's military, with fewer young entering the workforce. Examples include China and Germany.
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