GRR and NRR
The Gross Reproduction Rate
Exercise 1
Can you define precisely what is meant by a Total Fertility Rate of 2.4?
2.4 children would be born to each woman in a hypothetical cohort if she experienced the current age-specific fertility rates throughout her reproductive life, and survived to her 50th birthday.
The TFR is a measure of growth in the sense that if each couple replace themselves with more than two children, the population will grow (assuming mortality is low). However, if each woman only had male children, population growth would only last for one generation. We need to know how many children of the same sex replace the parent of the same sex in order to say something about longer term trends in population growth.
The Gross Reproduction Rate is similar to the TFR, but it is restricted to the number of girl children born to each woman in the hypothetical cohort of women if she experiences current ASFRs until the end of her reproductive life.
We do not always have data on the number of female children born to each age-group of women so we approximate this using the sex ratio at birth (which we assume to be 1.05 for most human populations)
| GRR | = |
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ƒ | x |
= |
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5 |
F | x |