Summary
Fertility is one of the big overarching topics of demography and it deserves serious study. Fertility is number of live births, not the medical concept of potential to conceive – that is fecundity.
We started this module with some simple measures of fertility. They all have their uses. The Crude Birth Rate is important because of its place in the demographic balancing equation, from which population growth can be calculated.
Age-specific fertility rates are important because they allow us to see patterns of fertility, which give us a good idea of both traditional and modern/early and late patterns of fertility. Patterns are important in demography!
The Total Fertility Rate (TFR) is very important because it is so widely used and quoted. It is derived directly from ASFRs and is a standardised measure which allows international comparisons. It is, by default, a period measure, although cohort TFRs are possible.
But the period TFR has tempo problems which non-demographers often do not appreciate and a further understanding of cohort fertility is also important. This itself has limitations but is a different way of viewing fertility and is important for that reason. Lexis diagrams help with visualising cohort fertility.
Parity progression ratios, in their simple form, are cohort measures and also provide a different appreciation of fertility – without tempo effects. They are particularly sensitive at identifying choice in childbearing.
Fertility is an area of demography where many theories exist to explain fertility change, especially focusing on how and why fertility decline commences. This is an interesting area but this module focuses on the technical assessment of fertility and the key measures that demographers must understand and know how to calculate and interpret.