The age/sex structure is also called the population pyramid. This structure or pyramid is a graphic way to show the age and sex composition of a population. The sum of all age and sex groups equals 100 percent of the population. Significant events in a population's history are visualized in a population pyramid. Events such as wars, baby booms, or periods of high in/out migration can affect the age/sex structure significantly.
This structure also predicts effects in a population. For example, if a population pyramid shows a bulge in the 10-19 age group, it is predicted that there will be a spurt of population growth over the next decade or two because the said age growth will enter their child-bearing years.