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MALES

FEMALES

AGE

# of population relative to scale

Population Pyramids tell a story of the past and predict the future

Watch THIS VIDEO for further understanding

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Types of Pyramids

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EXPANSIVE POPULATION PYRAMIDS

Expansive population pyramids show larger numbers or percentages of the population in the younger age groups, usually with each age group larger in size or proportion than the one born before it.

Population growth is rapid

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CONSTRICTIVE POPULATION PYRAMIDS

Constrictive population pyramids display lower numbers or percentages of younger people

Population growth is negative

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STATIONARY POPULATION PYRAMIDS

Stationary-or near stationary-population pyramids display somewhat equal numbers or percentages for almost all age groups . Of course, smaller figures are still to be expected at the oldest age groups.

Population growth is neutral or stable

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CONSTRICTIVE POPULATION PYRAMIDS

Constrictive population pyramids display lower numbers or percentages of younger people

Population growth is negative

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How to Read a Population Pyramid

Width of the Base-birth rate varies with the width of the base. A wide base indicates a high birth rate and a narrow base indicates a low birth rate

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Symmetry

Statistically speaking, pyramids should be relatively symmetrical
Any asymmetry indicates a difference in the male and female population
This pyramid shows more females at ranges above 50

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Shape of Sides

Concave sides indicate a high death rate convex sides indicate a low death rate
This population pyramid exhibits concave sides indicating a high death rate

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Bumps in the Sides

Irregularities in the sides indicate a demographic anomaly
The 30-50 age group in the US population pyramid represents the baby boom
The bump will travel upward as the baby boomers age

Irregularities in the sides indicate a demographic anomaly
The large numbers of working-aged men indicates migrant workforce

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Population Structure

Fertility and mortality vary not only from country to country but also over time within a country. As a result, the number of people in different age groups in a country form a pattern--the population structure

A country’s distinctive population structure can be displayed on a bar graph called a population pyramid. A population pyramid normally shows a percentage of the total population in 5 year age groups, with the youngest group (zero to four years) at the base of the pyramid and the oldest group at the top. The length of the bar represents the percentage of the total population contained in that group. Usually, males are shown on the left side of the pyramid and females on the right.

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Population pyramids vary widely within the United States. For example, Laredo, Texas, which has a large Hispanic population, has a relatively broad pyramid, indicating a large percentage of children, whereas Naples, Florida, has a “reverse” pyramid, indicating a large percentage of elderly people. College towns, such as Lawrence, Kansas, have unusually shaped pyramids because of the exceptionally high percentage of people in their 20s.

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Dependency Ratio...watch THIS VIDEO

The age structure of a population helps to understand similarities and differences among countries. One important way to compare the age structure among countries is the dependency ratio, which is the number of people who are too young or too old to work, compared to the number of people in their productive years. People who are 0-14 years of age and 65 and over are normally classified as dependents. The larger the dependency ratio, the greater the financial burden on those who are working to support those who do not. The dependency ratio is 47 percent in Europe, compared to 85 percent in sub-Saharan Africa.

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The high dependency ratio in sub-Saharan Africa derives from having a very high percentage of young people (see image in slide 6). Young dependents outnumber elderly ones by more than 14:1 in sub-Saharan Africa, whereas the number of people under 15 and over 65 are roughly equal in Europe. The large percentage of children in sub-Saharan Africa strains the ability of these relatively poor countries to provide needed services such as schools, hospitals, and day-care centers. When children reach the age of leaving school, jobs must be found for them, but the government must continue to allocate resources to meet the needs of the still growing number of young people. On the other hand, the “graying” of the population places a burden on developed countries to meet their needs for income and medical care after they retire from jobs.

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Sex Ratio

The number of males per 100 females in the population is the sex ratio. Developed countries have more females than males because on average women live seven years longer than men. Most Asian countries have more men than women, primarily because male babies outnumber female babies, especially in the two most populous countries, China and India (see image on next slide). The shortage of female babies in these countries has raised the possibility that a relatively large number of female babies are being aborted.