Demographic
Transition
Understand how birth rates, death rates, and population growth shift as societies industrialize and develop over time.
AP Environmental Science
What Is Demography?
Demography is the statistical study of human populations: their size, structure, distribution, and how they change over time through births, deaths, and migration.
Birth Rate (\( \text{CBR} \))
Number of live births per 1,000 people per year
Death Rate (\( \text{CDR} \))
Number of deaths per 1,000 people per year
\( \text{NIR} \)
Natural Increase Rate: \( \text{CBR} - \text{CDR} \)
Why Does Demographic Transition Matter?
The Demographic Transition Model (DTM) explains how populations shift from high birth and death rates to low birth and death rates as a country develops. It helps us predict:
1
Resource demand: How many people will need food, water, and energy?
2
Environmental impact: What will be the ecological footprint of a growing or aging population?
3
Economic planning: How will the labor force, dependency ratios, and healthcare needs change?
4
Policy decisions: Should governments encourage or discourage population growth?
Key Terms to Know
Total Fertility Rate
Average number of children a woman has in her lifetime. Replacement level: \( \approx 2.1 \)
Infant Mortality Rate
Deaths of infants under age 1 per 1,000 live births per year
Life Expectancy
Average number of years a newborn is expected to live under current conditions
Doubling Time
Estimated using the Rule of 70: \( t = \frac{70}{\text{growth rate (\%)}} \)
The Demographic Transition Model
Stage 1: Pre-Industrial
In Stage 1, both birth rates and death rates are high. Population growth is slow and fluctuates due to famine, disease, and war.
High \( \text{CBR} \)
No access to contraception; children are economic assets for farming
High \( \text{CDR} \)
Poor sanitation, limited medicine, frequent disease outbreaks
Stage 2: Urbanizing
Death rates drop rapidly due to improved sanitation, medicine, and food supply, but birth rates remain high. This creates a population explosion.
\( \text{CBR} \): Still High
Cultural norms haven't changed yet; large families still valued
\( \text{CDR} \): Falling Fast
Clean water, vaccines, hospitals, and agricultural revolution
Stages 3, 4, and 5
Stage 3: Industrializing
\( \text{CBR} \) drops as urbanization, education (especially for women), and access to contraception increase. \( \text{CDR} \) continues to fall. Growth slows.
Stage 4: Developed
Low \( \text{CBR} \) and low \( \text{CDR} \). Population stabilizes. Examples: USA, most of Europe, Australia.
Stage 5: Post-Industrial
\( \text{CBR} \) falls below \( \text{CDR} \). Population declines. Aging populations and labor shortages. Examples: Japan, Germany, Italy.
\( \text{CBR} \) vs. \( \text{TFR} \): Key Distinction
| Crude Birth Rate (\( \text{CBR} \)) | Total Fertility Rate (\( \text{TFR} \)) | |
|---|---|---|
| Definition | Births per 1,000 people | Avg. children per woman |
| Unit | Per 1,000 per year | Children per woman |
| Age structure? | No: affected by population age | Yes: controls for age |
| Replacement level | Varies by country | \( \approx 2.1 \) |
| Best for | Quick country comparisons | Predicting future growth |
The Rule of 70
This formula estimates how many years it takes for a population to double in size at a constant growth rate.
Example
Growth rate = 2%
Doubling time: \( \frac{70}{2} = 35 \) years
Doubling time: \( \frac{70}{2} = 35 \) years
Another Example
Growth rate = 0.5%
Doubling time: \( \frac{70}{0.5} = 140 \) years
Doubling time: \( \frac{70}{0.5} = 140 \) years
How to Apply the DTM
1
Find the \( \text{CBR} \) and \( \text{CDR} \) for the country in question (per 1,000 per year).
2
Calculate the \( \text{NIR} \): \( \text{NIR} = \text{CBR} - \text{CDR} \). Convert to a percentage by dividing by 10.
3
Determine the DTM stage by comparing \( \text{CBR} \), \( \text{CDR} \), and \( \text{NIR} \) to expected patterns.
4
Use the Rule of 70 if asked for doubling time: \( t = \frac{70}{\text{growth rate (\%)}} \).
5
Consider real-world factors: migration, government policies, epidemics, and economic shocks can alter expected trends.
Example 1: Identifying the Stage
1
Calculate \( \text{NIR} \): \( 42 - 18 = 24 \) per 1,000, or 2.4% annual growth.
2
Analyze: \( \text{CBR} \) is very high (42), \( \text{CDR} \) has dropped substantially from historical highs but is still moderate (18).
3
Conclusion: This matches Stage 2: death rate falling, birth rate still high, rapid population growth.
4
Doubling time: \( \frac{70}{2.4} \approx 29 \) years.
Example 2: Comparing Two Countries
| Country A | Country B | |
|---|---|---|
| \( \text{CBR} \) | 10 | 35 |
| \( \text{CDR} \) | 11 | 10 |
| \( \text{NIR} \) | \( 10 - 11 = -1 \) (decline) | \( 35 - 10 = 25 \) (rapid growth) |
| DTM Stage | Stage 5 | Stage 2 |
Example 3: Population Pyramids
Environmental Connections
Population growth directly affects environmental sustainability. The \( \text{IPAT} \) equation models this relationship:
\( I \) : Impact
Total environmental impact on the planet
\( P \) : Population
Number of people consuming resources
\( A \) : Affluence
Per capita consumption (GDP per person)
\( T \) : Technology
Impact per unit of consumption (efficiency)
Common Mistakes
✕ Confusing \( \text{CBR} \) and \( \text{TFR} \)
\( \text{CBR} \) counts births per 1,000 total people. \( \text{TFR} \) counts average children per woman. They measure different things and can move in different directions.
✕ Ignoring Migration
The DTM only models natural increase (births minus deaths). Immigration and emigration can dramatically alter a country's actual growth rate.
✕ Assuming Linear Progression
Not all countries follow the model at the same pace. Wars, pandemics, or policy changes (like China's one-child policy) can accelerate or reverse transitions.
DTM Summary
| Stage | \( \text{CBR} \) | \( \text{CDR} \) | Growth | Example |
|---|---|---|---|---|
| 1: Pre-Industrial | High | High | Low/Stable | None today |
| 2: Urbanizing | High | Falling | Rapid | Niger, Afghanistan |
| 3: Industrializing | Falling | Low | Moderate | India, Brazil |
| 4: Developed | Low | Low | Low/Zero | USA, France |
| 5: Post-Industrial | Very Low | Low | Negative | Japan, Germany |
Question 1 of 5
In Stage 2 of the Demographic Transition Model, what causes the population explosion?
In Stage 2, improved sanitation, medicine, and food supply cause death rates to drop rapidly, but cultural norms keep birth rates high. This widening gap between \( \text{CBR} \) and \( \text{CDR} \) creates rapid population growth.
Question 2 of 5
A country has a growth rate of 1.4%. Using the Rule of 70, approximately how long will it take this country's population to double?
Using the Rule of 70: \( \frac{70}{1.4} = 50 \) years. This is a straightforward application of the doubling time formula.
Question 3 of 5
Which of the following best describes a country in Stage 5 of the Demographic Transition Model?
Stage 5 is characterized by \( \text{CBR} \) falling below \( \text{CDR} \), resulting in a negative natural increase rate and population decline. Japan and Germany are classic examples.
Question 4 of 5
In the \( \text{IPAT} \) equation, what does the variable \( T \) represent?
In \( I = P \times A \times T \), \( T \) stands for Technology: the environmental impact per unit of consumption. More efficient technology reduces \( T \), lowering total environmental impact even as population and affluence grow.
Question 5 of 5
A country has a \( \text{CBR} \) of 12 and a \( \text{CDR} \) of 10. Its Total Fertility Rate is 1.6. What is the most likely DTM stage and why?
With low \( \text{CBR} \) (12), low \( \text{CDR} \) (10), and a \( \text{TFR} \) of 1.6 (below the 2.1 replacement level), this country is in Stage 4 or early Stage 5. The \( \text{TFR} \) below replacement suggests the population will eventually decline without immigration.