There's a lot more to know about populations than just how many people there are.Age - The age of a population can tell us a lot about what the population is doing, as well as what it will be doing in the future. A sudden increase in the birth rate (such as the post-world war "Baby Boom" in the United States) creates a "bulge" in the population. A larger than normal percentage of the population is then concentrated into a certain age group. As those people age, the bulge moves through the population and can have enormous societal effects. As baby boomers moved into middle age and started their own families, their tremendous purchasing power helped fuel the U.S. economy. As they move into old age, they will exert immense pressure on the health care industry and social security