# If immigration and emigration are ignored, what is the verbal equation for change in population size during a time interval?

boblawrence | Certified Educator

A verbal formula for change in population over a time period (disregarding immigration and emigration) would be as follows:

Population Change equals Number of Live Births minus Number of Deaths (the births and deaths occurring in the stated time period).

If births outnumber deaths, the population change is a gain.  If deaths outnumber births, the change is negative, or a loss.

Population growth rate is defined as the percentage of population change over time, expressed as a fraction of the initial population.

Example of Population Growth Rate Calculation:

World Population in 2006 = 6.7 Billion

World Population in 2011 = 7.0 Billion

Population Growth Rate = (7.0 – 6.7)/ 6.7  x 100 =  .3/6.7 x 100 = 4.47% (in 5 years) = .89% per year

As an interesting aside:  the world population is projected to reach 7 billion by this coming Halloween!