Teachers Guide for World Population Futures

Demographers develop population projections in an attempt to answer questions about our future. Forecasts of population size and characteristics allow city planners, economists, public agencies, environmentalists, and social scientists to prepare for what is to come.

Projections are based on current knowledge about population size and age structure, rates of birth, death, and migration, and assumptions about how quickly these rates will change.

The following activity introduces students to the process of projecting population growth and interpreting these changes. Students will simulate a projection of changing age composition in the United States and evaluate the results of different projection scenarios.

Grade Level: 9-12

Time Required: 2-3 class periods

Skills and Objectives:

• Ask questions about the utility of population projections
• Organize information by modeling population change
• Analyze information about population projections and population growth and change
• Answer questions about different scenarios of population projections

Vocabulary: projections, birth rate, death rate, net migration, cohort

Materials:

• World Population Futures (PDF: 338KB)
• Worksheet 1: The Cohort-Component Model: United States Simulation (PDF: 42KB)
• Worksheet 2: Projections of United States Population, 2000-2100 (PDF: 47KB)

Learning Activity

Background: Depending on the students' knowledge, you may need to introduce the concept of population projections and review other vocabulary.

Introducing the Activity: Introduce students to some of the reasons why population projections are needed. Select four students to each read one of the following scenarios and have the class respond. Use this as an opportunity to discuss what population projections are.

1. Schools: "I am from the local Department of Education. My job is to determine if we need to build a new school in the next 5 or 10 years. What type of information will I need to make this decision?" [Number of school age children predicted in the next 5 to 10 years]
2. Infrastructure: "I am a city planner. One of my responsibilities is to make sure we have enough roadways, water, sewers, and utilities. How will I know whether too many people will strain these resources in the coming years?" [Obtain projections of population growth]
3. Health Care: "I work for a company that establishes health care facilities. I must find out where a new center will be needed the most in the next 5 to 10 years." [Evaluate projections of places with a greater number of older people]
4. Environment: "I am an environmentalist working to make sure the habitat for wildlife in our area is not destroyed. If more people move here, the forest will have to be cut down so new homes can be built. How do I know if this will be a problem in 5 to 10 years?" [Obtain projections of population growth and migration]

Explain to students that they will be asked to make projections about the population growth of a simulated place. With these projections, what conclusions will they need to make about the future of their place?

Executing the Activity

1. Review with students the components of population change. Ask students to identify the three processes that lead to population growth or decline. What is the natural way a population grows? [Through births] What is the natural way a population declines? [Through deaths] What else cause a population to change? Does a population change through movement? [Migration] Show students the following equation:

Components of Population Change
 

2. Explain to students that if we are determining the future size of a population we need to know the current population size along with some assumptions about these components of change. How do we know the current population size? [From census and survey data] What criteria are used to make assumptions about levels of fertility, mortality and migration? [Reproductive behavior, childbearing trends, medical studies, life expectancy, and migration patterns]
3. Have students read the section in World Population Futures, "How Are Populations Projected?" Provide further explanation of the process.
   a. A population pyramid reveals the age and sex distribution of a population at one moment in time. The bars on the pyramid show the number of males or females in a particular age cohort.
   b. What will the population pyramid look like 5 years later? Look at figure below.
   

   Projecting a Cohort of U.S. Women Ages 15-19 in 2000 to 2005: The Cohort-Component Model Source: Data from U.S. Census Bureau. Adapted from J. Cohen, How Many People Can the Earth Support? (1995): figure 7.2.

   
   There are 9,672,000 females between the ages of 15-19 in 2000. In 2005, the number of females between the ages of 20-24 will be based on the population 15-19 in 2000 along with assumptions made about the number of deaths and migrants over the 5-year period. In the example, there were 115,000 deaths and 345,000 migrants in this age cohort. The result is 9,902,000 women ages 20-24 in 2005. [9,672,000 base population + 345,000 migrants - 115,000 deaths = 9,902,000]
   c. Using a calculator, have students complete the worksheet The Cohort-Component Model: United States Simulation and practice a simplistic version of the cohort-component model, approximating United States population in 2000 and 2005.
   d. Discuss with students how useful this process is. What are its strengths/weaknesses?

4. Point out to students that because of levels of uncertainty when making projections, demographers often offer alternative scenarios. Read World Population Futures, "Using Scenarios to Show Uncertainty." Different scenarios reflect variations in assumptions made about fertility, mortality and migration. Have students look at the different scenarios for population projections for the United States, developed by the U.S. Census Bureau. Use the worksheet Projections of United States Population, 2000-2100 or ask about the scenarios below. Ask students to evaluate the results of varying the components of population size.
   a. What does the medium projection assume the size of U.S. population will be by 2100?
   b. How does the projected population size of the U.S. population change if births are expected to decrease?
   c. What happens to population growth if there is a great increase in births by 2100?
   d. What is the projected population growth in a scenario of no immigration?

To see different projections of total population growth in the United States, use the worksheet Projections of the U.S. Population, 2000-2100.