As many high school students can confirm, you don’t need a crystal ball to make population projections. A pyramid will do instead. That’s because “population pyramids,” or age-sex distribution graphs, are really useful illustrations for showing the demographic make-up of a population (city, country, region, or world) over time, with clues to what it might look like in the future.
Classroom activities that engage students in creating and interpreting population pyramids have been a staple of Population Education’s curricula for middle and high school students for nearly four decades. Learning about, using, and understanding these pyramids are integral to two Advanced Placement courses: AP Human Geography and AP Environmental Science. Maybe that’s why our explanatory blog posts, “What is a Population Pyramid?” and “What Determines the Shape of a Population Pyramid?” continue to be two of the most downloaded items at www.populationeducation.org.
Demystifying Population Pyramids
A primer on population pyramids helps students understand what they are seeing. Most of us are used to viewing bar graphs with vertical bars. On a population pyramid, the bars are horizontal (males on one side; females on the other), each representing a cohort (age group, usually in five-year increments). Not all population pyramids look like pyramids, however. Populations with similar-size cohorts across the ages look more like rectangles (as is the case with many European countries), while rapidly growing populations in the least developed countries still retain a pyramid shape. This indicates a much higher percentage of younger people than older people.
So, what determines the shape of a population pyramid? Quite a lot. Events that took place during the 70-80 years depicted on the graph all have the potential to impact birth and death rates and thus, the graph’s shape. These “shaping” events might affect fertility (like the post-World War II “baby boom”) or longevity (like pandemics, wars, and natural disasters). Government mandates, like China’s “one-child” policy, also show up in the shape of a population pyramid.
Creating Pyramids in the Classroom
If time allows, we encourage teachers to have students construct population pyramids with the raw population data we provide for each cohort. “Power of the Pyramids” is an activity that we update regularly with the latest U.S. Census Bureau numbers for each cohort for a sampling of countries. We select countries that show students a variety of graph shapes, so they can make conclusions about how quickly or slowly a population might be growing. Using the total population for a given country, students calculate the percentages for each cohort. They are then ready to draw their graphs.
Once their graphs are completed, we discuss what they see. What are the largest cohorts for each of the countries? Why are there more elderly females than males in most of the graphs? Why are there more young boys than girls in some of the graphs? What does today’s population distribution indicate about the future population in the next 20-40 years?
For students of American history, we also have “Mysteries of the U.S. Pyramids,” which asks students to create and analyze the age-distribution graphs for different years in our nation’s history. For 1880, the U.S. pyramid looks much like a rapidly growing developing country today. The 1920 graph shows the ravages of World War I among the cohorts of young men. Jump ahead 40 years and the 1960 graph shows the much smaller cohorts of Depression Era babies (then ages 20-29) and the very large cohorts of baby boom kids. By 2000, our pyramid is stabilizing as our population ages, and by 2050, our graph has turned into more of a rectangle with a very large cohort ages 75 and older.
Part of the appeal of using population pyramid activities in the classroom is that they are interdisciplinary, employing math skills emphasized in today’s latest content standards (including Common Core). And, of course, they explore issues central to a range of social studies disciplines, including geography, economics, and history.
Downloadable versions of our two population pyramid activities are available at www.populationeducation.org, along with a short video demonstration of “Power of the Pyramids.” Also on the site are blog posts explaining the usefulness of age-sex distribution graphs and how they are used by students and demographers alike.