Declining Fertility Rates
Arnold Kling recently mentioned the declining fertility rates in Europe. I've been wondering for a while if perhaps this can be partially explained as a statistical illusion caused by women delaying (but not forgoing altogether) childbirth.
Calculating a nation's fertility rate necessarily involves some guesswork. For obvious reasons, it's not possible to know how many children a twenty-year-old woman will have over the course of her fertile life. But if we wait until she reaches menopause to count her children, then the fertility statistics will be perpetually out of date.
The method actually used to calculate the total fertility rate is to sum up the fertility rates for each age group. For example, suppose for the sake of brevity that women are fertile only between the ages of 23 and 27, and that in a given year we have the following birth rates:
Then the total fertility rate is .6 + .5 + .4 + .3 + .2, for a total of 2.0 children born to each woman over the course of her fertile life. This method works just fine as long as this pattern of birth rates doesn't change. But suppose that the women who are 22 this year decide to delay having children. Perhaps they decide that they want to follow a pattern like this, instead:
The women who are 22 this year will still average 2.0 children each over their fertile lives. But only 20% of them will have a child next year. So when we try to measure the fertility rate next year (remember that the women 24-27 are still following the old pattern), we get this:
Suddenly the fertility rate has dropped from 2.0 children per woman to 1.6. But this doesn't mean that fewer children will be born and the nation thrown into a population death spiral; it just means that their births will be delayed.
On the other hand, shifts in birth rates are not quite so abrupt in real-life, so it's quite possible that we will find thirty years from now that the current generation of Western Europeans have indeed chosen to reproduce at a below-replacement rate. But I do suspect that the fertility numbers exaggerate the magnitude of the problem, and that the 32-year population halving of which Dr. Kling speaks may not come to pass for those countries like Spain and Italy which ostensibly have fertility rates of around 1.3 today.
As an aside, why do Italy and Spain, two strongly Catholic countries, have the lowest fertility rates in Western Europe?
Update: More here.