Environmental Engineering Reference
In-Depth Information
Source: Population Matters
Doubling time
is the amount of time it takes for a population to double. It is also called the Rule of 70, be-
cause to find doubling time, 70 is divided by the annual percentage growth rate of a population. For example, a
population with a 3 percent growth rate will double in a little over 23 years (70 ÷ 3 = 23.3).
Demographic Transition
As the Western world has become more and more industrialized, there have been many shifts in birth and death
rates. In order to explain this, a model was developed by Frank Notestein in the 1940s and 1950s called
demo-
graphic transition.
Demographic transition moves from a pre-industrial stage, to a transitional stage, to an in-
dustrial stage, and ends in a post-industrial stage. Not all nations have or will pass through this demographic
transition; it's dependent on cultural and economic structures of each nation.
•
Pre-industrial stage:
Death and birth rates are high due to poor medical care, extensive disease, diffi-
culty in acquiring food, and people having many children because of high infant mortality. The popula-
tion of people is relatively stable.
•
Transitional stage:
Death rates start declining because of medical advancements and better food produc-
tion. Birth rates remain high, leading to large population growth.
