Which statement about age structure diagrams is true?

• A. They show higher population density in urban areas
• B. They help predict future population changes by revealing age-and-sex distribution
• C. They measure life expectancy directly
• D. They track only male populations

Answer: (B)

Age structure diagrams, or population pyramids, illustrate how many individuals exist in each age group and, for each group, the number of males and females. This layout highlights fertility and survivorship patterns and helps us see how a population is likely to change over time. The reason this statement is the best is that the shape of the diagram reveals future potential: a broad base with many young people signals potential for continued growth as those cohorts reach reproductive age, while a narrow base with fewer young people suggests slower growth or possible decline. Seeing both sexes across age groups also helps anticipate future dynamics, such as changes in the sex ratio that can affect reproduction and social planning. These diagrams do not directly measure life expectancy—that information comes from life tables and mortality rates across ages. They also do not indicate population density in urban areas, since density is a geographic measure, not an age-and-sex composition. And they include both sexes, not just males.