## Population Growth Rate

Demographers, scientists who study population dynamics, define the growth rate of a population as the amount by which a population's size changes in a given time.

Whether a population grows, shrinks, or remains the same size depends on four processes: birth, death, emigration, and immigration. Immigration (iM-uh-GRAY-shuhn) is the movement of individuals into a population, and emigration (EM-i-GRAY-shuhn) is the movement of individuals out of the population. Two of these processes—birth and immigration—add individuals to a population, while the other two processes—death and emigration— subtract individuals from the population. For simplicity's sake, demographers usually assume that immigration and emigration are zero when calculating a population's growth rate. By making this assumption, they can describe a population's growth rate in mathematically simple terms.

### Population Size

It is customary for demographers to divide large populations into groups of 1,000 and to present data per capita, meaning per individual. Birth rates, death rates, and growth rates for a large population are usually expressed per capita. For example, if there are 52 births and 14 deaths per 1,000 individuals in a large ro population in one year, the birth rate would be joy, or 0.052 births per capita per year. The death rate would be yyy0, or 0.014 deaths per capita per year.

The growth rate can be found by the following simple equation:

birth rate - death rate = growth rate