POP: Lesson - Age-Structure Diagrams (Topic 3.6) 📖

⏳ Estimated Reading Time: 8 - 10 minutes

Learning Objective

Explain age-structure diagrams.

 

Age-Structure Diagrams

Age-structure diagrams (also known as population pyramids) provide a way for us to look at the entire population of an area and visualize what the population might look like in the future or has looked like in the past.  Each “bar” on the population profile is a cohort of individuals in the same age group. These diagrams are usually broken into male and female members of each cohort, so we can also see if the distribution of males and females changes over time.

Explore the presentation below to learn more about the basics of age-structure diagrams. Once you understand the parts of an age-structure diagram, see if you can point out each part in the diagrams in the next section:

Essential Knowledge

Population growth rates can be interpreted from age structure diagrams by the shape of the structure.

 

Increasing Population Sizes - Expansive 

Countries with populations that are increasing tend to have population profiles that have a wide base and a skinny top, similar to the shape of a triangle. These countries are known as underdeveloped or developing countries, depending on their social and industrial progress and their pyramids are known as expansive age-structure diagrams.

Explore the expansive population pyramid below to discover the characteristics of populations in these countries:

The image shows a 2016 population pyramid for Tanzania. Two sets of bars on either side of a central axis represent age groups from 0-4 years at the bottom to 100+ years at the top. The blue bars on the left depict males, and the red bars on the right depict females. Bar width represents population size in millions. The graph shows a larger young population, decreasing with age, typical of a developing country.
You can tell a lot about a population based on the shape of the population pyramid. What does the shape of this pyramid tell you about Tanzania?

Open each tab below. They explain what you can tell by the shape of an expansive population pyramid:

🪦 Death Rate (click to reveal)

Tanzania has a HIGH death rate. You can see this in the "skinny" top of the pyramid, indicating that few individuals live to old age.

        • The life expectancy in Tanzania is 67 years old, which is quite low.
        • The median age is 17, indicating that half the population is 17 years old or younger.
        • The child mortality rate for children under 5 is 54 out of every 1000 children.
💰 Economics (click to reveal)

High death rates often indicate LOW INCOMES.

        • The Natural Bureau of Statistics states that the monthly household income in Tanzania was about $443/month in 2017/18.
🏥 Medical Care (click to reveal)

Countries with high death rates often lack access to MODERN MEDICAL CARE.

🚰 Clean Water (click to reveal)

Countries with high death rates often lack access to CLEAN WATER.

        • Only about 50% of the population has access to clean water.
        • Only about 24% of the population has access to improved sanitation.
🍼 Birth Rate (click to reveal)

Tanzania has a HIGH birth rate. You can see this in the wide base of the pyramid, indicating many individuals in the population are young.

🏭 Industrialization (click to reveal)

Countries with high death rates often lack access to MODERN NECESSITIES.

        • 67% of the population does not have electricity.
🚺 Women (click to reveal)

Countries with a HIGH birth rate have a HIGH fertility rate.

        • The fertility rate for Tanzania is 4.9 children per woman.

Countries with HIGH birth rates have LOW contraceptive use and FEW years of schooling.

        • Only 38% of women in their reproductive ages on birth control.
        • Females only have an average of 5.2 years of schooling.

 

Essential Knowledge

A rapidly growing population will, as a rule, have a higher proportion of younger people compared to stable or declining populations.

 

Steady Populations - Stationary

Countries with populations that remain fairly steady tend to have population profiles that are more rectangular in shape, which is known as a stationary age-structure diagram.  The sides of these diagrams tend to be fairly straight. These populations have similar amounts of children and middle-aged members of the population.  The tops of these profiles are still small because people tend to die as they get older.  These countries have birth rates that tend to cancel out the death rates. Explore the stationary population pyramid of the United States from 2018 to see some characteristics of populations with similar birth and death rates:

Explore the stationary population pyramid to discover the characteristics of populations in these countries:

The image depicts a 2018 population pyramid for the United States. Blue bars on the left represent males, red bars on the right represent females. Age groups range vertically from 0-4 years at the bottom to 100+ years at the top. Bar width indicates population size in millions. The pyramid shows a decreasing population with age and a wider base, indicating a larger younger population.
You can tell a lot about a population based on the shape of the population pyramid. What does the shape of this pyramid tell you about the United States?

Open each tab below. They explain what you can tell by the shape of a stationary population pyramid:

🪦 Death Rate (click to reveal)

The United States has a LOW death rate. You can see that while the very top of the pyramid is "skinny" (no one lives forever), indicating that more individuals live to old age.

        • The life expectancy in the United States was 78.7 years old, which is quite high.
        • The median age is 38.2, indicating that half the population is at the end of their reproductive years.
        • The child mortality rate for children under 5 is 5.6 out of every 1000 children.
💰 Economics (click to reveal)

Low death rates often indicate HIGH INCOMES.

        • The Natural Bureau of Statistics states that the monthly household income in the United States was about $5161/month in 2017/18.
🏥 Medical Care (click to reveal)

Countries with low death rates often have access to MODERN MEDICAL CARE.

🚰 Clean Water (click to reveal)

Countries with low death rates often have access to CLEAN WATER.

        • 96.97% of the population has access to clean water.
        • 99.4% of the population has access to improved sanitation.
🍼 Birth Rate (click to reveal)

The United States has a LOW birth rate. You can see this in the small base of the pyramid, indicating fewer individuals are born.

        • The birth rate in the United States decreased 2% in 2018 to a record low.
🏭 Industrialization (click to reveal)

Countries with low death rates often have access to MODERN NECESSITIES.

        • 0.1% of the population does not have electricity.
🚺 Women (click to reveal)

Countries with a LOW birth rate have a LOW fertility rate.

        • The fertility rate for the United States was 1.92 children per woman, declining from 3.02 in 1976 and 2.07 in 2008.

Countries with LOW birth rates have HIGH contraceptive use and MANY years of schooling.

        • 65% of women in their reproductive ages are on birth control
        • Females have an average of 13.8 years of schooling, indicating that at least half of the women age 25 and older have completed grades K-12 and have some post-high school education.

 

Declining Populations - Restrictive

Countries with populations that are decreasing tend to have smaller bases and larger tops, similar to an inverted pyramid. These pyramids are known as restrictive.

These populations have much fewer children than middle-aged (reproductive) members of the population. They still have few older individuals because people tend to die as they get older.  This shape indicates that even though there are enough people of reproductive age, they are not having children, as evidenced by the small number of children.  These populations will decrease in size eventually because there won’t be as many people of reproductive age when the small numbers of children grow up. Italy is a country famous for its declining population. When this happens, people like to say the population is graying, because the population will soon have more older people than younger.

Explore the restrictive population pyramid of Italy from 2018 to see some characteristics of populations with negative growth:

The image displays a 2018 population pyramid for Italy. Blue bars on the left represent males, red bars on the right represent females. Each bar represents an age group's population, with males dominant in younger age groups and females dominant in older ones. This pyramid visually represents Italy's population distribution by age and gender in 2018.
You can tell a lot about a population based on the shape of the population pyramid. What does the shape of this pyramid tell you about Italy?

Open each tab below. They explain what you can tell by the shape of a restrictive population pyramid:

🪦 Death Rate (click to reveal)

Italy has a HIGHER death rate than birth rate. You can see that while the very top of the pyramid is "skinny" (no one lives forever), there are more older individuals than younger individuals.

        • The life expectancy in Italy was 83.28 years old, which is quite high.
        • The median age is 42.7, indicating that half the population has passed their reproductive years.
        • The child mortality rate for children under 5 is 3.1 out of every 1000 children.
💰 Economics (click to reveal)

Low death rates often indicate HIGH INCOMES.

        • The Natural Bureau of Statistics states that the monthly household income in Italy was about $2249/month in 2018.
🏥 Medical Care (click to reveal)

Countries with low death rates often have access to MODERN MEDICAL CARE.

🚰 Clean Water (click to reveal)

Countries with low death rates often have access to CLEAN WATER.

        • 95.82% of the population has access to clean water.
        • 95.82% of the population has access to improved sanitation.
🍼 Birth Rate (click to reveal)

Italy has a LOW birth rate. You can see this in the small base of the pyramid, indicating fewer individuals are born. Italy has one of the LOWEST birth rates in the WORLD.

🏭 Industrialization (click to reveal)

Countries with low death rates often have access to MODERN NECESSITIES.

        • 0.1% of the population does not have electricity.
🚺 Women (click to reveal)

Countries with a LOW birth rate have a LOW fertility rate.

        • The fertility rate for Italy was 1.33 children per woman in 2018.

Countries with LOW birth rates have HIGH contraceptive use and MANY years of schooling.

        • 69.3% of women in their reproductive ages are on birth control.
        • Females have an average of 10.6 years of schooling, indicating that at least half of the women age 25 and older have completed at least 10 years of school.

 

AP Exam Tip

Steady populations tend to have age-structure diagrams shaped like a rectangle, due to having similar birth and death rates.

Populations with triangle-shaped age-structure diagrams are usually underdeveloped or developing countries with high birth and death rates.

Declining populations have age-structure diagrams shaped like an inverted triangle, due to low birth rate and death rates.

 

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