Tempo-Adjusted Fertility

The period total fertility rate sums the age-specific fertility rates observed in a single year, treating them as if a synthetic cohort experienced them. When women across society shift their childbearing to older ages, the births that would have occurred this year are pushed into future years, so the rates observed now are temporarily thinner at every age. The synthetic-cohort sum therefore falls below the number of children women will actually have — a tempo distortion, not a real drop in quantum. When postponement stops, the rate recovers, sometimes overshooting, even though completed family size never changed.

Postponement and its pace differ across parities: the timing of first births may be moving rapidly while higher-order births shift more slowly, and the mean ages and their rates of change are order-specific. Applying a single adjustment factor to all-order fertility would blend these distinct timing shifts and distort the correction. Computing an order-specific change in mean age and adjusting each order's TFR before summing keeps each parity's tempo distortion handled with its own factor, which is central to the Bongaarts-Feeney formulation.

No. The tempo-adjusted TFR is a hypothetical period quantum: it estimates the level the period rate would show if there were no change in the timing of births this year, under the assumption that order-specific schedules shift without changing shape. Completed cohort fertility, by contrast, is the actual average number of children born to a real cohort of women over their lifetimes. The two are related but distinct, and they can differ when the constant-shape assumption fails or when quantum itself is changing across cohorts.