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The Total Fertility Rate (cont.)

Replacement level

The TFR is often referred to in the context of “Replacement Level”. This is a figure that represents the level of TFR at which the population, in the long run, would remain the same size – not grow or shrink. This is popularly taken to be a TFR of 2.1. The thinking behind this is that if every woman (on average) produces two children in her lifetime then roughly half will be girls and these girls will replace their mother and produce children themselves, which will sustain the population. A slight margin on the TFR (2.1 rather than 2) allows for the fact that some girls will not survive to become mothers.

In fact demographers can produce more accurate figures than the universal 2.1, given a knowledge of mortality and the sex ratio at birth. Clearly in high mortality situations a TFR of rather more than 2.1 might be necessary.

This calculation will become apparent in later sessions that deal with Reproductivity (PAPP103_S06), but suffice it to say here that the commonly quoted replacement figure of TFR=2.1 is an approximation, but in general an acceptable one given modern levels of mortality.

In very high mortality situations 2.1 would be an under-estimate.