Most modern demographic analysis is framed by the , which describes the historical shift from high birth and death rates to low ones as societies develop.
: The actual reproductive performance of a population. Demographers measure this through the Total Fertility Rate (TFR) —the average number of children a woman would have in her lifetime. Currently, the world is nearing the "replacement level" of 2.1, below which a population eventually begins to shrink.
: Death rates fall due to better sanitation and medicine, while birth rates remain high, leading to rapid population growth. Demography: The Study of Human Population
: High birth and death rates; population size remains stable but low.
: Both rates are low; the population stabilizes. Most modern demographic analysis is framed by the
: The incidence of death in a population. Improvements in healthcare and nutrition have led to a significant increase in global life expectancy, which rose by over eight years between 1995 and 2026.
: Birth rates fall below death rates, leading to an aging and potentially shrinking population—a stage now characterizing many advanced economies like Japan and Italy. Currently, the world is nearing the "replacement level" of 2
: Birth rates begin to fall as society urbanizes and education (especially for women) increases.