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MODULE 9

Population Dynamics

Demographic Net migration:
LEARNING GOALS Natural change: Accounting Equation
births minus deaths In-migration minus

9-1 Explain how the world’s population has Births Out-migration In-migration
grown over time.
9-2 Explain how we measure birth rates.

9-3 Explain how we measure death rates .
level of population
9-4 Explain how we measure natural increase.

Deaths migration
According to the Merriam-Webster Dictionary,
dynamics means “a pattern or process of change,
Out-
growth, or activity,” so population dynamics refers to
the growth and change of the human population on
Earth. Births and deaths are the two most basic demo- Figure 9.1 The basic demographic equation. Can you think
graphic events that change the population size. Births of a few circumstances under which the population of a place
may grow rapidly?
add people to the population, and deaths do the oppo-
site. If we want to see how a country’s population has Population at beginning of period
risen or fallen in a year, we need to calculate the differ- + Total births
ence between total births and total deaths in that coun- + Total in-migrants
try in that year. The result is the net change, or natural - Total deaths
increase. We also need to consider the effects of migra- - Total out-migrants
tion, including how many people moved in (in-migrants) = Population at end of period
and how many moved out (out-migrants). Here then we
have the basic demographic equation that reveals the In this Module, we focus on the natural increase com-
total population change of a country or place. If we add ponent of population dynamics, the key concepts related to
the total number of births and in-migrants during a births and deaths. The migration component of population
period (usually a year) to the beginning-of-the-period change will be covered in Modules 15–17 in this Unit.
population, and subtract the total numbers of deaths
and out-migrants during the same period, we derive 9-1 How has the world’s population grown
the-end-of-the-period population (Figure 9.1): over time?
Human Population Growth
TERMS TO KNOW . . . over Time

demographic equation: The method for calculating total
population of a country or place based on natural increase Before we discuss the key concepts related to births and
and migration over a period of time (usually a year). deaths, it is helpful to look at how the human popula-
tion has grown over time.
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