Let’s now explore the different fertility rates and what they have to say.
Let’s now explore the different fertility rates and what they have to say.
The general fertility rate is measured differently from the birth rate. The birth rate’s denominator is the mid-year population, but the general fertility rate’s denominator is the mid-year population of females of child-bearing age.
The denominator should indicate what number of people in the population are (typically) capable of giving birth.
Age-specific fertility rates (ASFR) give even more precision as to the age of mothers. For example, the (age-specific) fertility rate for females 15 years old = number of live births to 15 year-olds during the year divided by the mid-year population of female 15 year-olds, all multiplied by 1000.
In Figure 11-1, each line represents a different cohort of mothers. The top, dark blue line is for women born in 1946. They experienced their highest fertility when they were 24 years old. This does not mean that women born in 1946 had their first child at age 24. It means that women born in 1946 were more likely to have a baby at age 24 then at any other age, whether to the first, second, or higher order child. Since the late 1970s, the average age of mothers in Canada has been rising. As the dark red line shows, women born in 1975 had their highest fertility at age 30. We cannot yet tell at what age women born in 2000 will have their highest fertility. Not enough time has gone by for them to complete their fertility experience.
Once a woman, or a group of women born the same year, is no longer of child-bearing age, we record how many children were actually born to that woman or that cohort of women. We can compute the completed fertility rate (CFR).
For example, for Canadian women born in 1946, the completed fertility rate was 2.1, i.e. 2.1 children per woman. This includes women who never had children.
But that is looking into the past. To get an idea of how many children today’s women will have, demographers compute a hypothetical statistic called the Total Fertility Rate. The total fertility rate is the number of children which would be born to the average woman IF the average woman will experience today’s age-specific fertility rates at each age of her life.
Just as life expectancy at birth for infants today is calculated assuming that infants today will have today’s age-specific mortality rates as they go through life, TFR today assumes that today’s young women will go through their lives bearing children at today’s age-specific fertility rates. So, TFR is hypothetical, an estimate based on today’s age-specific fertility rates.
where ASFR is age-specific fertility rates, and n represents the number of years in each age category. Age groups are usually 5 years in length e.g. 15-19, 20-24, 25-29 etc.
Why do we divide by 1000? Well, the ASFR gives you the number of children per 1000 women of that age, say 130 children. Now one woman cannot have 130 children. Only 1000 women can. So we divide by 1000 to get the number of children per wom