The world is a complicated place

[Cutlass]

Any figures for that? Seems hard to believe.

Guttmacher favors abortion rights, but the abortion statistics it gathers are the most detailed available and are widely cited by both sides in the debate. And regardless of whether the abortion ratio is 33 or 30 or 22 percent, Santorum cannot assume that those aborted fetuses reduced the U.S. population by an equal number of people — which is what he suggests when linking abortions to Social Security’s financial problems. In an e-mail, Wind said that "most women obtain abortions to postpone childbearing not to prevent it altogether," and noted that some of the aborted pregnancies "would have ended in miscarriage."

Wind, March 31: The group of women most likely to have an abortion are in their early 20s. They may already have one child and don’t want another at that time, or they may be childless but desire to have children in the future. Either way, the abortion postpones the birth of their child, it does not eliminate it — and there is no impact on the overall population. Some abortions actually terminate pregnancies that would have ended in miscarriage, so again you can’t assume that every abortion would have otherwise resulted in a live birth.

http://www.factcheck.org/2011/03/santorum-wrong-on-abortion-birth-facts/

It was mentioned in the Freakanomics article on the subject and others have mentioned it, but I don't have access to the original study.

Edit: Here is a RAND study who finds the results that birth rates for whites would be about 3% higher with an abortion ban, and 5% higher for blacks.

Implications for Public Policy
Extrapolating these statistical results to a lifetime concept such as TFR is, admittedly, far from precise. Nevertheless, these data do show that abortion policy has only moderate effects for white fertility but larger effects for black fertility. The results imply that there has been some substitution from other forms of contraception (and abstinence) to abortion. In other words, pregnancies that might have been prevented by contraception are now being aborted instead. The net effect of abortion legalization and Medicaid funding therefore appears to explain little of the decline of American fertility since 1970.

These results have implications for welfare reform. An explicit goal of welfare reform is to lower nonmarital fertility without increasing abortions. Klerman's work suggests that Medicaid funding of abortions would help cut nonmarital fertility but only at the cost of increasing abortions. With respect to welfare policy, these goals thus appear to be in conflict.

 

[Flying Pig]

Ah, interesting. I suppose it does encourage more people to say 'stuff it, if I get pregnant we can always have an abortion', of which some of those will then change their minds.

 

[Cutlass]

And many who intend to have children will find themselves pregnant at a time that just does not work out. Too young, or ill at the time, or something like that. But then go on to have children later in a more planned fashion.