Population Pyramid Analysis

An expansive pyramid is wide at the base and tapers steeply, signalling high fertility, higher mortality, and a young, rapidly growing population typical of early-transition countries. A stationary pyramid is roughly rectangular up to old age, indicating near-replacement fertility and low mortality with little growth. A constrictive pyramid is narrow at the base and bulges higher up, the signature of sustained below-replacement fertility and an ageing population. Real countries often show hybrids, and the change in shape across censuses is itself the key signal.

Placing males to the left and females to the right of a shared age axis lets you compare the two sexes at every age at a glance. This makes sex imbalances immediately visible — for example, an excess of young adult men from labour in-migration, or an excess of older women from women's longer life expectancy. A single combined bar would hide these patterns, which are often the most policy-relevant features of the structure.

Not directly, but its shape carries strong information about momentum. A population with a very wide base will keep growing for decades even if fertility falls to replacement, because large young cohorts have yet to reach childbearing age — this is population momentum. To turn the current structure into an actual forecast you must apply a cohort-component projection that ages each cohort forward under assumed fertility, mortality, and migration rates; the pyramid is the starting condition, not the forecast itself.