
World in the Balance


Classroom Activity

Objective
To calculate how long it takes a country's population to double in size and to
investigate factors affecting growth rate.
 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
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.
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.
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.
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.
Explain to students that they will be using 10year compounded growth rates
to determine when each country's population will double. The 10year 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.
Use the steps on the "Calculating Population Growth" student handout to
demonstrate how to calculate future population sizes using the growth rate
data.
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 xaxis in increments of 10 and the number of
individuals on the yaxis in increments of five. Then ask students to
draw the bestfit curve.
If necessary, help students see that population growth is not a
linear function; i.e., it produces a curved graph rather than a straightline
graph. Have teams answer the questions on their student handouts and hold a
class discussion about their conclusions.
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.)
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).
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 twopage report on its
findings. Students can find some of this information in the CIA World Factbook,
the World Bank Group Data Profile tables, and CountryReports.org at
www.cia.gov/cia/publications/factbook/
www.worldbank.org/data/countrydata/countrydata.html
www.countryreports.org/
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 lowgrowth rate countries? Among highgrowth rate
countries? What are some of the differences between the factors among
lowgrowth rate and highgrowth rate countries?
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 studiesbased activities—one on global warming and the
other on U.S. immigration—in our Educational Role Plays at
www.pbs.org/nova/worldbalance/roleplay/
Countries with high growth rates double more quickly than those with low growth
rates. Highgrowth 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
Country 
10year
compounded growth rate

Population
doubles after approximately:

Australia 
0.097 
80
years (105)

Bangladesh 
0.226 
40
years (113)

Brazil 
0.121 
70
years (111)

Cameroon 
0.221 
40
years (111)

Canada 
0.098 
80
years (106)

Cayman
Islands

0.317 
30
years (114)

Chad 
0.353 
30
years (124)

China* 
0.062 
120
years (103)

Colombia 
0.168 
50
years (109)

Costa
Rica

0.167 
50
years (108)

Egypt 
0.204 
40
years (105)

Ghana 
0.155 
50
years (103)

Guatemala 
0.300 
30
years (110)

Guinea 
0.264 
30
years (101)

Haiti 
0.180 
50
years (114)

Hong
Kong

0.128 
60
years (103)

India 
0.157 
50
years (104)

Kenya 
0.134 
60
years (106)

Kuwait 
0.389 
30
years (134)

Madagascar 
0.348 
30
years (122)

Malta 
0.075 
100
years (103)

Mayotte 
0.516 
20
years (115)

Mexico 
0.126 
60
years (102)

Nepal 
0.251 
40
years (122)

New
Zealand

0.114 
70
years (106)

Norway 
0.044 
160
years (100)

Pakistan 
0.220 
40
years (111)

Saudi
Arabia

0.379 
30
years (131)

Singapore 
0.400 
30
years (137)

Somalia 
0.402 
30
years (138)

Uganda 
0.339 
30
years (120)

United
States

0.096 
80
years (104)

Uruguay 
0.082 
90
years (102)

Vietnam 
0.137 
60
years (108)
 *Note:
China has a governmentcontrolled birthrate.
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 10year 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 lowgrowth rate
country might be concerned with having enough workers to sustain a strong
economy and support the nation's seniors; a leader of a highgrowth 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 10year 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.
Web Sites
NOVA Web Site—World in the Balance
www.pbs.org/nova/worldbalance/
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
www.earthday.net/goals/issues.stm
Explains the major threats to our environment, including water pollution,
deforestation, and global warming, and offers opportunities for taking
action.
Ecological Footprint Quiz
myfootprint.org
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
www.worldbank.org/depweb/english/modules/social/pgr/
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
www.unfpa.org/issues/index.htm
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
www.prb.org/
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
www.pbs.org/sixbillion/
Includes a study guide on population and the perspectives of people from six
different countries.
The World Bank Group: Data by Country
www.worldbank.org/data/countrydata/countrydata.html
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
www.census.gov/cgibin/ipc/popclockw
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
esa.un.org/unpp/
Generates population statistics, for the world or for individual countries, for
a given time period. Also gives a list of developed and lessdeveloped
countries.
Books
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 TwentyFirst 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 58

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:
Algebra
Data Analysis and Probability
Grades 912

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:
Algebra
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.

