The quantum effect of fertility refers to the total number of children a woman has over her reproductive lifespan, usually captured by the Total Fertility Rate (TFR). It stands in contrast to the tempo effect, which reflects when births occur. A woman delaying childbirth may lower the period TFR (a tempo effect), even if her eventual completed fertility (quantum) remains unchanged. The distinction is critical in demography but also deeply relevant to economics and evolutionary biology.
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