I know this is one of your favorite topics so I have a question. I know the replacement number of chidren is 2.1 per woman. Is that figure calculated using only women of childbearing age (defined however) or total adult women? or total females? What is the denominator?

Total number of women. I.e., the average number of children every woman should have during her lifetime is 2.1 in order to keep the population stable.

2.1 based on 2 children needed to replace the father and mother and .1 to deal with people that die early due to disease, accidents, etc.

As for Scotland the article notes that most of the immigrants were from the new EU countries (Poland, Czech, etc). As long as they don't mind wearing kilts it shouldn't be an issue.

Few people are aware that there is a long tradition of Polish bag pipes. I forget hpow it is different from the Scottish ones, but similar enough to be mistaken at first glance.

Come to think of it, the 2.1 is only valid assuming a 50/50 split between boys and girls; if the split were 60/40 it would be more like 2.6 to maintain.

If it is total women, then would an aging female population skew the statistics? Total women could increase while total children remained the same - causing the average to drop. That might still result in a population decline but it would be more of a short-term leveling off rather than a continuous decrease.

Brandon -

Yes, but then the younger cohort of women would have to make up for it; i.e. produce 2.6 (say) children per nubile woman, and there is no evidence they are doing this. If the younger cohort starts to again produce 2.1, then the population will stabilized, but decreased.

Ahem. That last sentence should read, "..will be stabilized, but decreased."

Bruce,

I don't think your point is really different from mine. It does seem obvious that Europe is headed for a population decrease (among native Europeans anyway.) I'm just wondering if the statistics don't point toward a slight decrease more than a drastic one.

Plus, since the child replacement rates I've seen run from 1.3-2.0, at what point would an aging effect no longer be important? I was hoping someone here could point me to a more in-depth statistical analysis.

Brandon--I think you've mistaken what the statistic is. It is not (#children/#women), but rather (#children/1 woman's lifetime), so there isn't any aging effect.

Brandon:

http://www.overpopulation.com/faq/basic_information/total_fertility_rate/

Suppose population were to stay the same but forty years from now 90% of those under 50 were Muslims and Eastern Europeans? What's left of France, Germany, Scotland, etc.?

Brandon - If the birth rate is 1.4 per woman, 2.1 is replacement, and the average age at which the mother gives birth is 30, then every 30 years the number of mothers declines by 1/3. After 90 years, the population of birth-mothers has declined to 8/27 of what it used to be, for a 70% decrease.

b,

Well it actually turned out to be average number of babies born to women during their reproductive years. So you're right, there doesn't seem to be an aging effect there. I do wonder how they determine that figure though?

OJ,

Thanks for the link. I don't know what will become of France, etc, but the site projected a decrease in all nations, not just European ones. So fewer immigrants will be coming into Europe

Brandon:

How does that follow? Would you stay in Somalia or go take over an empty Holland?

Brandon: I am very curious how you think a woman could have children during her non-reproductive years...

OJ,

Immigrants have to come from a pool of people. If that pool is smaller, then the number of immigrants will be smaller. So do you think that Europe is going to stay filled with people, but Africa is going to empty out? Besides, I hear Somalia is lovely this time of year.

b,

Definitions are the key to statistics. They must be precise. Otherwise this stuff happens:

http://archives.tcm.ie/irishexaminer/2003/04/10/story489834519.asp

So what? That just shows that we're getting to the point where medicine can make a woman's reproductive years equal to her lifetime minus the first dozen years or so. If all of a sudden in Ireland every 66 year old woman starts having kids, you better count them in your total fertility rate if you want to accurately predict demographic trends...

Brandon:

Yes, there'll be more people and less Europeans.

Brandon -

I think in my previous post, I answered a different question than the one you asked...

Total Fertility Rate must be computed using only childbearing years, else the scenario you described due to aging would indeed have to be accounted for (although it wouldn't be too hard if the older cohort doesn't radically increase its lifespan compared to previous generations).

I found much more info than anyone could ever want at this link:

http://www.health.state.pa.us/hpa/stats/techassist/fertility.htm

Roughly, they use ages 15-44 for computation.

I will note the example in the link bemoaned the fact that 1996 (the last year of measurement) had the lowest TFR in Pennsylvania since 1950!