The Total Fertility Rate (cont.)
What does the TFR actually measure?
The TFR is defined as:
The number of children a woman would have if she lived from age 15 to age 50 and experienced the ASFRs of the period in question.
The phrase "would have" suggests the measure is theoretical – and indeed it is! It is an example of a synthetic cohort; it is not the experience of a real cohort moving from year to year. The measure (usually) relates to a single year and another novel way of defining it would be:
The number of babies produced by 35 women, one of each single age 15-49, living through the single year to which the TFR refers.
This is a more cumbersome definition – and is NOT a conventional definition - but does demonstrate that the measure is a snapshot of the babies produced in a single named year if the population structure was one single woman of each single-year age and experiencing the current ASFR for her age.
The measure is an abstract one – one that has been directly age-standardised using a standard population of 1 woman in each age group – but is the more useful and internationally comparable for that standardisation.