Human populations grow and shrink due the balance between *births* and *deaths*. The number of births per 1000 people is called the **birth rate**, and the number of deaths per 1000 people is the **death rate**.

**The Population Growth Rate**

Population growth rate = birth rate β death rate

Itβs really not a complicated equation, you must admit. Say the birth rate of Switzerland was 23/1000 and the death rate 28/1000. The population growth rate works out as **-5/1000** (23/1000 β 28/1000). As a percentage, this is** -0.5%** growth. This means that there is a **net decrease** of 5 people per thousand.

**The Demographic Transition Model**

This is a model used to classify different populations depending on their birth rate, death rate, overall population size, and the factors behind these numbers. There are 5 different…