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World in the Balance

Classroom Activity


To calculate how long it takes a country's population to double in size and to investigate factors affecting growth rate.

Materials for each team
  • copy of the "Double Up" student handout (PDF or HTML)
  • copy of the "Calculating Population Growth" student handout (PDF or HTML)
  • copy of the "Growth Rates Worldwide" student handouts (PDF or HTML)
  • calculator
  • graph paper
  • access to print and Internet resources

  1. Since 1800, human population has grown from one billion to six billion people. Over the next half century, that number is projected to rise to nine billion. Tell students that in this activity they will investigate how long it takes the populations of different countries and territories to double.

  2. Before class, refer to the "Growth Rates Worldwide" student handouts to create a list of six to eight countries for each team. Try to make sure that each team's list includes countries with a range of growth rates and that the class data set represents countries on all of the continents (excluding Antarctica, which has no indigenous population). Choose countries with a growth rate of more than 0.044 to ensure that the rate will double in a reasonable time frame (Norway, with a rate of 0.044, takes 160 years to double; Japan, with a rate of 0.011, takes 630 years). See Activity Answer for some sample doubling rates. Don't choose countries with negative growth rates as they will never double.

  3. Organize the class into teams of four and provide copies of the student handouts and other materials to each team. Assign each team its set of countries.

  4. Define the meaning of growth rate: the increase in a country's population during a period of time expressed as a percentage of the population at the start of that time. For example, if a town had 75 people in 1980 and 100 people in 1981, the growth rate for the year would be 33 percent.

  5. Explain to students that they will be using 10-year compounded growth rates to determine when each country's population will double. The 10-year growth rate is based on annual growth rates from 2003 from the U.S. Bureau of Census International Database. The starting population for each country will be 50 individuals, and for this activity the growth rate will be assumed to be constant.

  6. Use the steps on the "Calculating Population Growth" student handout to demonstrate how to calculate future population sizes using the growth rate data.

  7. After teams have doubled the populations of all of their assigned countries, have teams graph their countries' population growths. Have students put the number of years on the x-axis in increments of 10 and the number of individuals on the y-axis in increments of five. Then ask students to draw the best-fit curve.

  8. If necessary, help students see that population growth is not a linear function; i.e., it produces a curved graph rather than a straight-line graph. Have teams answer the questions on their student handouts and hold a class discussion about their conclusions.

  9. Create a class histogram on the blackboard, posterboard, or an overhead to compare population doubling for each country. The histogram will need to have an upper time value of the country that takes the longest to double and should have an upper population size value of 150. Ask each team to represent each of its countries with a data point and an abbreviation of the country's name. Examine the histogram with students. Where do most of the countries in the class data set fall on the histogram? What else do students observe about the histogram? (Remind students that this does not represent all the world's countries.)

  10. Have students brainstorm a list of factors they think might affect growth rate (e.g., birthrate, death rate, access to medical care, nutrition, immigration, education, and income).

  11. Ask students to choose the four lowest and the four highest growth rate countries among their data sets or from the larger data table representing all the countries. Organize the class into teams belonging to two groups: Have one group use print and Internet resources to research some factors that contribute to low growth rates and the possible environmental, social, and economic impacts on the people within those populations; have the other group research factors contributing to high growth rates and the corresponding impacts on people in its populations. Have each team write a two-page report on its findings. Students can find some of this information in the CIA World Factbook, the World Bank Group Data Profile tables, and at
  12. To conclude the lesson, discuss with students some of the factors affecting growth rates in the countries they researched. Do students see any commonalities among low-growth rate countries? Among high-growth rate countries? What are some of the differences between the factors among low-growth rate and high-growth rate countries?

  13. As an extension, have students choose countries with a negative growth rate and calculate the time it takes for a population to decrease to half its original size given an initial population size of 100 individuals. Then have them research reasons for negative growth rates.

Additional Activities
Find two social studies-based activities—one on global warming and the other on U.S. immigration—in our Educational Role Plays at

Activity Answer

Countries with high growth rates double more quickly than those with low growth rates. High-growth rate countries have higher birthrates and lower deathrates. The greater the difference between birthrate and deathrate, the more quickly the population grows.

The following table provides sample results for the amount of time it takes for a population to double. The numbers in parentheses are the calculated values for total population size at that period in time. All numbers are rounded up.

Sample Population Doubling Rates


10-year compounded
growth rate

Population doubles
after approximately:



80 years (105)



40 years (113)



70 years (111)



40 years (111)



80 years (106)

Cayman Islands


30 years (114)



30 years (124)



120 years (103)



50 years (109)

Costa Rica


50 years (108)



40 years (105)



50 years (103)



30 years (110)



30 years (101)



50 years (114)

Hong Kong


60 years (103)



50 years (104)



60 years (106)



30 years (134)



30 years (122)



100 years (103)



20 years (115)



60 years (102)



40 years (122)

New Zealand


70 years (106)



160 years (100)



40 years (111)

Saudi Arabia


30 years (131)



30 years (137)



30 years (138)



30 years (120)

United States


80 years (104)



90 years (102)



60 years (108)

*Note: China has a government-controlled birthrate.

Sample Graph: United States

Sample graph: United States

Most student graphs should indicate that growth rate is a curve rather than a straight line; however, for countries with a growth rate close to zero (i.e., Germany, Japan, and France), students may not have enough data points to show a curved line. In these cases, you may wish to have students calculate and plot more data points and/or extrapolate the shape of the line based on other graphs. In this activity, doubling the growth rate results in the population size doubling in approximately half as much time.

Greenland and South Africa have the lowest 10-year compounded growth rate (0.001) and would take 6,890 years to double. Montserrat has the highest growth rate (0.553) and would take 20 years to double. A leader of a low-growth rate country might be concerned with having enough workers to sustain a strong economy and support the nation's seniors; a leader of a high-growth rate country might be concerned with providing adequate services—such as education, health care, and jobs—for a large population. World population would double in about 60 years if the projected 10-year growth rate is 0.123.

There are numerous factors that contribute to low and high growth rates. Tell students that while it is possible to generalize factors affecting population size, these generalizations may not be accurate. Each country has a unique set of circumstances. Countries with negative or low population growth rates tend to have low fertility rates and low female illiteracy rates. In the case of Botswana, however, a high fertility rate is offset by a high infant mortality rate. Countries with relatively high population growth may have high fertility rates and high female illiteracy rates (as in the case of Chad).

Other factors that influence the population growth rate of a country include life expectancy, health care, access to fresh water, sanitation, and level of technology.

Links and Books

Web Sites

NOVA Web Site—World in the Balance
In this companion Web site to the NOVA program, find the latest population figures, see how the world's population has grown, learn about how rising populations affect the environment, test your understanding of population trends, read interviews with experts, discover ways to get involved, and more.

Earth Day Network
Explains the major threats to our environment, including water pollution, deforestation, and global warming, and offers opportunities for taking action.

Ecological Footprint Quiz
Estimates how much land and water you need to support your lifestyle. Enables you to compare your footprint to other people's and to the amount of resources available on Earth.

Population Growth Rate
Provides a general background on factors affecting population growth rate and some of the problems that may develop if a population grows too quickly.

Population Issues Overview
Offers an overview of some of the factors related to population issues such as access to family planning, poverty, and lack of education and choices for women.

Population Reference Bureau
Contains articles, datasheets, and reports regarding population issues. Information is arranged by regions and by topics, including family planning, gender, and health.

Six Billion and Beyond
Includes a study guide on population and the perspectives of people from six different countries.

The World Bank Group: Data by Country
Provides data such as population, fertility rate, literacy rate, and other figures related to population for different countries, regions, and income levels.

World POPClock Projection
Gives the U.S. Bureau of the Census' daily estimate for the total world population and provides a link for more POPClocks.

World Population Prospects
Generates population statistics, for the world or for individual countries, for a given time period. Also gives a list of developed and less-developed countries.


Bouvier, Leon F. and Jane T. Bertrand. World Population: Challenges for the 21st Century. Santa Ana, CA: Seven Locks Press, 1999.
Provides a history of population growth and covers issues ranging from immigration to family planning.

Fyson, Nance Lui. World Population. New York: F. Watts, 1998.
Examines the effects of agricultural, industrial, and medical factors on population growth.

Mazur, Laurie Ann. Beyond the Numbers: A Reader on Population, Consumption, and the Environment. Washington, DC: Island Press, 1994.
Presents essays reflecting eight population and consumption issues. Topics include gender equality, family planning, and reproductive rights.

Menzel, Peter. Material World: A Global Family Portrait. San Francisco: Sierra Club Books, 1994.
Presents the material possessions of average families throughout the world, featuring a photo of each family posing outside their home with all of their material goods surrounding them.

Newbold, K. Bruce. Six Billion Plus: Population Issues in the Twenty-First Century. Lanham, MD: Rowman & Littlefield Publishers, 2002.
Explores various impacts on population including HIV and AIDS, fertility, and immigration.


The "Double Up" activity aligns with the following National Science Education Standards and Principles and Standards for School Mathematics:

Grades 5-8

Science in Personal and Social Perspectives

Science Standard F:
Science in Personal and Social Perspectives

Populations, resources, and environments:

  • When an area becomes overpopulated, the environment will become degraded due to the increased use of resources.

  • Causes of environmental degradation and resource depletion vary from region to region and from country to country.

Mathematics Standards:
Data Analysis and Probability

Grades 9-12

Science in Personal and Social Perspectives

Science Standard F:
Science in Personal and Social Perspectives

Population growth:

  • Populations grow or decline through the combined effects of births and deaths, and through emigration and immigration. Populations can increase through linear or exponential growth, with effects on resource use and environmental pollution.

  • Various factors influence birthrates and fertility rates, such as average levels of affluence and education, importance of children in the labor force, education and employment of women, infant mortality rates, cost of raising children, availability and reliability of birth control methods, and religious beliefs and cultural norms that influence personal decisions about family size.

Mathematics Standards:
Data Analysis and Probability

Classroom Activity Author

Margy Kuntz has written and edited educational materials for 20 years. She has authored numerous educational supplements, basal text materials, and trade books in science, math, and computers.

Teacher's Guide
World in the Balance

Video is not required for this activity
Park Foundation, Sprint, Microsoft
Park Foundation Sprint Microsoft

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