Final answer:
The age that divides a population in half with regard to age is the median age. It provides a single index that summarizes the age distribution and is affected by various factors like birth rates and increased life expectancy.
Step-by-step explanation:
The age that divides a population into two numerically equal-sized groups, where half the people are younger than this age and half are older, is known as the median age. When statisticians calculate the median age of a population, they are finding that middle number that reflects the age distribution of a population. For example, if the median age in the United States is around forty, this indicates that approximately half of the population is under forty years old, and the other half is over forty.
As the median age rises, it suggests that the population is aging. This could happen for several reasons such as a decline in birth rates or increased life expectancy, leading to a larger proportion of older individuals. To understand this change over time, one might look at historical data, such as how the median age of the U.S. population increased from 30.0 years in 1980 to 33.1 years in 1991. This rise in median age does not necessarily mean that the number of children decreased; it could also be influenced by other demographic factors, such as the aging of a large cohort, like the Baby Boomers.