This lesson reinforces the idea that Earth's population, including the population of the United States, is gowing at a dramatic rate. It discusses some of the basics of demography, the study of population and its changes, and introduces key terms used to describe a population. The lesson inlcudes an activity in which students use an online reference to look up some population statistics and answer questions related to them. Educational levels: Undergraduate lower division, High school

John Pratte

Ken Rhinehart

English

Digital Library for Earth System Education

 
Population: Basic Statistics 
Introduction 
 
For all of its futuristic stylings, the television show Star Trek was, like most science fiction, a commentary 
on the state of society at the time it was written (late 1960’s).  One of the more famous episodes of that 
series was the one entitled The Mark of Gideon, which dealt with a planet that was so overpopulated that 
people did not have anywhere to sit down.  At the time of the show, the Earth’s population was at about 
3.5 billion, and was increasing at an incredible rate.  The effects of such a large population on the 
environment were beginning to become abundantly clear, and people had begun to wonder just how 
many more people the Earth could hold.  This Star Trek episode was just one of a number of television 
shows, movies, and books at that time (ex. Soylent Green) that foretold of an ominous future if we did not 
begin to do something. 
 
Since that time, the only thing that seems to have changed is that the world’s population has gotten 
larger.  We now have more than 6.3 billion occupants, and we are continuing to grow.   Not only that, but 
the United States population is growing dramatically, meaning that US citizens may someday need to 
make a decision about how much is too much and then develop a policy, if it were possible, to control 
growth.  
 
Demographic Basics 
 
Demographers are researchers who study population and its changes. Some terms that they use are birth 
rate, death rate, replacement-level fertility, and total fertility rate. We will discuss them here: 
 
Birth rate:  Commonly used as the crude birth rate, this is the number of births per 1,000 people within a 
certain population. 
 
Death rate:  Commonly used as the crude death rate, this is the number of deaths per 1,000 people 
within a certain population. 
 
The formulae for determining crude birth rate and crude death rate for a given time interval, such as a 
year, are as follows: 
 
total number of births in a population      x      1,000     =     crude birth rate                 
               total population 
 
total number of deaths in a population     x      1,000     =     crude death rate 
               total population 
 
Replacement-level fertility: This is the average number of births couples in a population must have in 
order to keep the population stable at a certain number. In more developed countries, this number is 
approximately 2.1. In any human population, the replacement-level fertility always exceeds 2.0 because 
some offspring do not make it to the age of 15, which is the age demographers define as the beginning of 
the reproductive years; therefore, more offspring are needed to cover for the shortfall. In less developed 
countries, the replacement-level fertility is higher than 2.1 because of harsher conditions and increased 
childhood mortality. 
 
Total fertility rate: This is the average number of children a woman in a population has in her lifetime. 
Excluding immigration and emigration from the equation, if the total fertility rate exceeds the replacement-
level fertility in a population, then the population is growing. If the total fertility rate is below the 
replacement-level fertility, then the population is reducing. Germany, for example, is a growing in 
population only because of immigration because its total fertility rate is well below replacement-level 
fertility. 
 
An excellent web site for finding statistics related to population is the following: 
 
http://www.geographyiq.com  
 
When you arrive at the site, click on where it says “Rankings” on the menu at the upper left. When you 
arrive at the next web page, scroll down until you see the “Population” topic heading. You will see 
categories related to population such as birth rate, death rate, and total fertility rate listed. Statistics for 
each country in the world are provided. 
 
Determining in Percentage Terms How Fast a Population is Growing or Declining 
 
Here is the formula for determining how fast a population is growing or shrinking annually: 
 
Annual Rate of              =           Births      -      Deaths          x               100      =       X% 
Population Change                                1,000 
         
We all learned at one time or another that we can simply a formula by crossing out zeroes in the 
numerator and denominator, so we are left with the following version: 
 
Annual Rate of             =            Births     -      Deaths            =                X% 
Population Change                                  10   
 
Example: Let us say that a certain population has 28 births and 8 deaths per 1,000 people in that 
population for a certain year. How fast is that population growing or shrinking for that year? 
 
Annual Rate of             =               28          -         8                =                 2 % 
Population Change                                  10 
 
The population is growing at 2% per year. 
 
Doubling Time and the Rule of 70 
 
Mathematicians are so smart. In economics, they found that if one divides an annual percentage rate into 
a certain number, then the number of years for that amount to double could be determined. Likewise for 
population, if the growth rate is divided into the number 70, then the number of years it would take for the 
population to double could be precisely determined if the growth rate stays the same from year to year; 
hence, a population growing at 1% per year would take 70 years to double. 
 
Example: A population of 10 million is growing 3.5% per year. If it stays at this rate from year to year, how 
many years would it take for the population to reach 20 million? 
 
70        =         20 years 
3.5 
 
Yes, it is that simple to figure. If the population grows consistently at 3.5% per year, then 20 years is all 
the time it takes for the population to double. 
 ESA21: Environmental Science Activities Activity Sheet Population Basic Statistics 
Name: 
 
To answer the following questions, go to http://www.geographyiq.com and click on “Rankings” that you 
see in the menu on the left.  Look at the list under the title Rankings and find Population. Look to the right 
of the word Population and click on the link labeled “All Descending”. You will then see a list of the 
countries of the world and their populations.  Answer the following questions: 
 
1. Which is the most populous country in the world? 
 
 
2. Of the two most populous countries, in fraction terms, approximately how much of the world’s 
population do these two most populous countries comprise if world population is 6.3 billion? Circle the 
correct answer. 
 
one eighth   one sixth   one third  one half 
 
3. Using 6.3 billion, what percentage of the world’s population belongs to the United States? Circle the 
correct answer 
 
2%   5%   8%   10% 
 
4. Click on “Rankings” in the menu at the left of the http://www.geographyiq.com web site. You will see 
under the title Rankings “Birth Rate” and “Death Rate”.  Go to those web pages to get the following 
information: 
 
Country Birth Rate Death Rate 
Germany   
Somalia   
United States   
Mexico   
China   
 
5. Using the formula for calculating annual rate of population change that you read in the lecture part for 
this activity, use the information in the table above to determine the change for the countries below. If the 
population has a higher death rate than birth rate, be sure to show a negative value for population 
change. 
 
Country Annual Pop. Change (X%) 
Germany  
Somalia  
United States  
Mexico  
China  
 
6. Go back to the list under the title “Rankings” at http://www.geographyiq.com and click where it says “All 
Ascending” next to Population growth rate (Note: You can still get the same information from “All 
Descending”; the information is simply listed in reverse).  Find the listed population growth rate for 
Germany. How does the growth rate shown for Germany there compare with Germany’s annual rate of 
population change that you calculated above? How much do they differ? 
 
 
7. Why do these numbers differ? In other words, what is taken into account when they calculated the 
population growth rate that you found for Germany as opposed to the growth rate that you calculated for 
Germany just using the birth rate and death rate numbers? Without this factor, would Germany still be 
growing? 
 
 
 
 
 
 
 
 
 
 
 
 
Population Explosion or Not? 
 
8. Based on what you’ve noticed from observing the population statistics for countries of the world, what 
can you say about what is happening with population in general around the world: 
 
the population explosion is continuing world-wide 
population is now showing a negative growth rate (reduction) in approximately 95% of the countries in the 
world 
population is stable world-wide with total fertility rates equaling replacement-level fertility, neither growing 
nor shrinking significantly 
some countries are still growing at a high rate, but other countries have total fertility rates well below 
replacement-level fertility 
 
Total Fertility Rate and Replacement-Level Fertility 
 
9. On the “Rankings” web page found at http://www.geographyiq.com , find Total Fertility Rate in the list 
under Rankings. Click on the link All Ascending that you see to the right of Total Fertility Rate. 
 
 Which country in the list comes closest to equaling the replacement-level fertility of 2.1? 
 
 
10. Which country has the fewest number of children born per woman? 
 
 
11. Regarding the highly populated countries of India and China, find the total fertility rates of the two 
countries. Based on those figures, which of the two countries has been more effective in decreasing its 
total fertility rate? 
 
 
 
12. Looking at the list of the countries and their total fertility rates, which countries can you generalize to 
be less stable politically: those with low total fertility rates or those with high total fertility rates? 
 
 
 


Population: Basic Statistics

http://esa21.kennesaw.edu/activities/populationstats/populationstats.pdf

Population: Basic Statistics

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