This data from the Guttmacher Institute shows why the idea that abortion bans achieve nothing is a myth

One of the most compelling arguments against restrictions on access to abortion is that these laws don’t stop abortion, but just drive it underground.

Although this is commonly accepted in ideological circles, there’s surprisingly scant evidence to support it at all. In fact, data from the Guttmacher Institute — a pro-choice research body best known for propagating this myth — contradicts this.

Restrictions against abortion do, in fact, reduce the likelihood that a woman will abort

The argument that abortion restrictions don’t reduce abortion is broadly based on the premise that regions that have banned abortion have higher abortion rates. This is indisputably true. As you can see below, there is a strong correlation between living under restrictive abortion laws and a higher overall abortion rate:

A more reasonable measure is the percentage of pregnancies that end in abortion. If your average Nigerian woman, for example, is several times more likely to get pregnant than an Icelandic woman, it seems disingenuous to suggest that a higher abortion rate in Nigeria means Nigerians are more likely to abort.

When you instead compare abortion law restrictiveness to proportion of aborted pregnances, you actually get an inverse correlation.

Given this, is it really fair to conclude — per the Guttmacher Institute — that “restricting access to abortions does not reduce the number of abortions”? Not really.

The next problem is that looking at rates on a regional level is fundamentally misleading because cross-regional comparisons make it very difficult to control for all the other factors that influence the abortion ratio: cultural attitudes to abortion, the acceptability of child-bearing outside of marriage, economic resources, religiosity etc. When you repeat the above analysis by country within the same region, you get an even more striking result.

The only region, as broken out by the Guttmacher Institute, with significant levels of law variation is Northern Europe. Given the similarities between Northern European countries, do we see a correlation between abortion law and the abortion ratio? Yes.

Note that Ireland has one of the lowest abortion ratios in the entirety of Europe; these figures include even those Irish women who travel to the U.K., Holland or other countries in Europe to obtain an abortion.

Of course, the best kind of analysis is not simply cross-regional or cross-country but focused on a single country over time. What does the data here tell us?

Countries that restrict abortion see a decline in the likelihood of aborting, while countries that do the opposite see an increase

We have relatively good data for some Eastern European nations. With the Communist takeover of Eastern Europe, several economically similar countries liberalized their abortion laws at a similar time. The corresponding rates in Bulgaria and Czechoslovakia — which kept better records than other Soviet-sphere countries — saw a substantial increase in their abortion ratio:

At this point, you still might be skeptical. If abortion is illegal, why shouldn’t we just think that the procedure — and its reporting — is just driven underground? This is reasonable objection and, fortunately, it has a reasonable response: fertility rates.

Fertility rates measure a legal procedure at all points in time: giving birth. If abortion is made illegal in a country, you should expect to see an increase in the fertility rate. (This should only happen in a country where there is little existing stigma around abortion; in 2006, when Nicaragua banned abortion, it did not see a corresponding increase in its fertility rate as the abortion ratio was already low.) Conversely, a liberalization of abortion laws should lead to an decline in fertility rates.

The pro-choice psychologist Henry David, who lobbied Eastern European governments to liberalize their abortion laws and argued that abortion did not have a negative effect on women’s mental health, summarized the data as follows:

“Although the fertility effects of abortion law modifications need to be considered within the context of related social legislation and previously established demographic trends, the experience in Central and Eastern Europe strongly suggests that the fertility-suppressing effect of abortion liberalization was substantial.”

This effect is heightened when the ban is accompanied by a ban on contraception. Otherwise, couples can mitigate a rise in fertility by adjusting their sexual behavior or using contraception.

This pattern is particularly noticeable in the example of Romania, which, over the course of the 20th century, ricocheted between vastly differing abortion policies. In 1966, the Communist state banned abortion as well as contraception. With the banning of abortion, and the banning of one mechanism for controlling fertility, we see a huge spike in the fertility rate:

In countries with both elevated abortion rates and continued access to contraception, you see a small but temporary spike in the fertility rate:

We see a similar pattern in the United States, in those states that banned abortion, prior to the 1972 Roe vs. Wade ruling. Dr. Joanna N. Lahey, an economist from Texas A&M, summarizes her studies of abortion laws as follows. I was not able to find the full data set upon which her work relies, but she summarizes her research as follows: