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 But if we wait until she reaches menopause to count her children, then the fertility statistics will be perpetually out of date.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:

Age Birth Rate
23 60%
24 50%
25 40%
26 30
27 20%

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:

Age Birth Rate
23 20%
24 30%
25 40%
26 50
27 60%

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:

Age Birth Rate
23 20%
24 50%
25 40%
26 30
27 20%

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.

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John Kennedy over at

John Kennedy over at no-treason raised the point one time that there's no logical reason to care about whether people replace themselves. I'm curious, do you agree Brandon Berg, or do you think the people in these countries have some kind of obligation to reproduce more if the rates have indeed declined?

Brandon, have I mentioned

Brandon, have I mentioned that you rock? About three weeks ago I made a note to myself after reading an alarmist Mark Steyn column on this subject that I should examine the actual data because I had a hunch that it was being overblown. You've given a really good lead here, thanks.

Stefan: No, I don't think

No, I don't think anyone has an obligation to reproduce. In fact, I'm hoping that in my lifetime radical life-extension therapy will become available, making low fertility a moot point. But if it doesn't happen, and if fertility really is below replacement, then there might be problems, particularly if governments insist on trying to maintain old-age welfare programs.

Sort of, but you did so in a way that implied that I was a woman.

"As an aside, why do Italy


Because they’re staunchly Catholic? Add their birth rates to the out of wedlock birthrates in less Catholic countries and you get close to the actual birth rates in those less Catholic countries.

Nah, probably not, only an idea.

In the long run, I think

In the long run, I think delayed births = fewer births. If you shrink the practical length of time devoted to childbearing by whatever means, one can expect fewer births from the individual woman, regardless of age.
I also think that women who make the conscious decision to delay pregancy want fewer children.

Brandon, Your simplification


Your simplification has a problem. The actual fertility rate is live births per woman who is at least past puberty over her lifetime. With in-vitro fertilization, menopause no longer limits fertility. The calculation is done using actuarial techniques based upon actual ages of women at the actual point of giving birth and is adversely affected by "therapeutic" abortions and actual childlessness related to sexually transmitted diseases, economics, and other factors in the decisions of women to give birth.

The replacement rate is always greater than two simply because not all live births live long enough to reproduce, are capable of reproduction, or actually do reproduce. To me, an interesting question is the slope of the replacement rate over time. I believe that the curve has a negative slope and is now near its practical minimum. The currently low rate of pre-pubertal mortality certainly reduces the incentives to have children, while the reduced maternal mortality rate increases the incentives to delay childbirth.


You are correct. Historically, child bearing began as soon as possible after puberty generally 14 or so. Today, the average age of menarche is 11 in developed countries, but the average age of first live birth is well into the 20's. Physically, the best age for live birth is 19 to 24. Live births by women younger than 18 or older than 30 greatly increase the risks.

It is not generally realized by the public, but athersclerosis begins in your teens for most of us and at much younger ages for those with familial hypercholesterolemia associated with hyper-apolypoproteinemia type E (high LDL/VLDL/lypoproprotein A...typing this from memory from the work I did in with pathologists in 1981).

Fertility is the

Fertility is the age-specific expectations and wishes among women in fertile ages - cultural determined. No changes without greater changes in the prevention, abortions, postponements caused by education, economic self-selfsufficiency and alike.

Birth quotients: is the number of children divided with number of women in the fertile ages in a specific period, eventually calculated age-specific - Determined by fertilty, age-distribution among other things and immigration.

I the following you have the real problems connected to information
recently made public:

Information of Denmark

Why not report the real fertility or real birth rates of Europe?

I know the ethnic fertility is perhaps not accounted for in your country, but sooner or later it will be much easier to tell the truth. It is also easier not to have to take especially good care every single time you mention the subject in a special neutral formulation: “Women in Germany” “Frauen in Grossbritannien“

According to:


I am sorry about the following table

Tabel 1: Total fertility and calculated
ethnic fertility in some European countries


Total fertility
Calculated 1)

Ethnic fertility


Spain ”off.” earlier












Great Britain


25 EU-countries

15 old EU-countries

Source to total fertility:

Eurostat: page 16

1) Calculation of ethnic fertility in some European countries:

When we add the number of immigrants from areas outside Western Europe, North America, Israel, Japan, Australia and New Zeeland included the naturalized and their children to the official accounted number of in this category 1 January 2006, we get a smaller number than reality, because the naturalized earlier than 1979 and their descendants are not included in the account from , Databanken.


The reasons to include the naturalized and descendants:




In average all immigrants from less developed countries load the public sector three times as much compared with the Danes (according to newly report from the Danish Velfare Commission), and the second and third generation load the public sector even heavier.

The number of immigrants from the selected area is the only number that has been growing - even accelerating growing and also exponential in periods - for all the last 25 year.








Our future - of interest:




