The Total Fertility Rate (cont.)
Period and Cohort; Tempo and Quantum
Let’s explore the TFR a little deeper. Firstly, the term “TFR” invariably means “period TFR” unless otherwise stated. It is derived from a synthetic cohort and represents a measure derived from data for a particular period – usually a single year. Like all period measures things can change from year to year and the measure will also change. In the developed world children are expensive commodities and in periods of economic hardship or strife families delay having children although they may fully intend to do so when things improve.
Figure 5 shows a time series of TFRs for France and you can see the year-on-year variability. In some periods this is quite extreme: during the First World War, immediately following the Second World War, and the steep decline in the early 70’s. So here is one problem of the TFR – it is highly variable and can change rapidly from one year to another.
Figure 5. France: total period fertility rate by year
