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Monday, August 25, 2014

Contraception, abortion, and the importance of control groups.

Some pro-lifers point out that many women seeking abortion were using (or misusing) some type of contraception when they conceived. Sometimes pro-lifers cite this fact as evidence that contraception does not decrease, and may even increase, abortion.

But this conclusion is misguided. It seems likely that women who don't want to be pregnant are more likely both to use contraception and to seek abortion than women who actively want to be pregnant or women who are ambivalent about pregnancy. If that's the case, we have a correlation/causation problem.

Which means I get to use an XKCD comic in my blog post!

In order to talk about whether contraception increases, decreases, or has no effect on abortion, we need to look at studies that have control groups. Ideally, a control group is identical to the experimental group in every way except for the one factor you want to analyze. As my beloved Wiki explains:
Scientific controls allow an investigator to make a claim like "Two situations were identical until factor X occurred. Since factor X is the only difference between the two situations, the new outcome was caused by factor X."
In the case of contraception and abortion, ideally we would have research that compares a control group of women to an experimental group of women. The two groups would be identical in terms of relationship stability, financial status, beliefs about abortion, feelings about pregnancy, and any other relevant factors. The control group of women would use no contraception, and the experimental group of women would use contraception. Then we could compare the rates of unplanned pregnancy and abortion for each group, and we could more reasonably talk about how contraception affects abortion rates.

A big part of the contraception debate is whether contraception actually decreases unplanned pregnancies. One side cites research showing the rate of unintended pregnancies is much lower for sexually active people who use contraception than for those who don’t.

The other side counters that not everyone would necessarily be as sexually active if contraception wasn’t so widely available. This side talks about risk compensation – the idea that if people believe contraception makes sex less risky, those people will make riskier sexual decisions. For example, they may choose to have sex more frequently, in less committed relationships, or with less careful attention to the woman’s cycle.

The fact that many women who have abortions were using contraception when they got pregnant doesn’t tell us anything about how contraception affects pregnancy rates. To illustrate the problem, here is a hypothetical situation using entirely made up numbers:

Suppose we have two groups of 100 women each. The first 100 women, called the Nope group, really don't want to be pregnant. 90% of them use contraception, and 100% of them will choose abortion if pregnant. The second 100 women, called the Meh group, are either open to or ambivalent about pregnancy. 10% of them use contraception, and 17% of them will choose abortion if pregnant.

Each symbol represents 10 women.

Now let's say 20 of the Nope women and 60 of the Meh women get pregnant, so 20 of the Nope women and 10 of the Meh women choose abortion. So 30 women are abortive.

If 90% of Nope and 10% of Meh used contraception.

For simplicity, let's assume their abortion decisions aren't related to whether they used contraception, so 90% of abortive Nope women (18 women) and 10% of abortive Meh women (1 woman) were using contraception. That means 19 out of the 30 abortive women were using contraception when they got pregnant, or 63% of abortive women were using contraception when they got pregnant!

Yet, in this scenario, contraception did greatly decrease pregnancy rates. The Meh women were three times as likely to get pregnant as the Nope women. If, like the Meh women, only 10% of the Nope women used contraception and 60 of the Nope women got pregnant, all 60 of those Nope women would have chosen abortion. Then there’d be 70 abortions instead of 30.

If 10% of Nope and 10% of Meh used contraception (scenario 1).

From this perspective, using contraception decreased abortions by 57%!

Yay contraception!

Alternatively, what if less contraception meant less risky sexual choices? Suppose again only 10% of Nope women use contraception, but this time suppose they’re so careful about sex that only 10 of them get pregnant. Then there'd be only 20 abortions instead of 30.

If 10% of Nope and 10% of Meh used contraception (scenario 2).

In this scenario, not using contraception decreased abortions by 33%!

Boo contraception!

The point is, without control groups, we don't know which way it would go. We can (and do) have strong opinions about how we think it would play out, but until we cite research with control groups, we're really just guessing. Simply saying "most of the women who got abortions had been on birth control" doesn't tell us one way or another how the abortion rates would be if less women used birth control.


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That doesn't mean the fact is irrelevant. If nothing else, we know contraception alone will not eliminate abortion. And I think it's true that there are plenty of pro-choice people who implicitly understand this idea, and see abortion as the "safety net," a back up form of birth control.

But there's a big difference between saying "contraception won't fully eliminate abortion" and "contraception makes no difference in abortion rates" or even "contraception increases abortion rates." The point about abortive women using contraception only speaks to the first statement, not the second two statements. For those statements, you need more information.

38 comments:

Matt Cash said...

Great post! I'll be sharing this with my page!

conversate said...

Aren't teen pregnancy and even abortion rates highest in the bible belt?

Anyway, some pro lifers lose credibility when they protest clinics that only hand out BCP:
http://www.cosmopolitan.com/politics/news/a29520/planned-parenthood-richfield/

Robert said...

What do you think of the St. Louis CHOICE Project's work?

In a follow-up communication they noticed while handing out free birth control to thousands of women in St. Louis that the St. Louis Planned Parenthood had a significant reduction in abortions performed while Planned Parenthood clinics in the area and in Kansas City stayed the same.

http://journals.lww.com/greenjournal/Citation/2013/04000/Perinatal_Outcomes_Associated_With_Obstructive.27.aspx

JDC said...

I just saw a xckd comic in a Secular Pro-life blog post. Day officially made.

Guest said...

Teen pregnancy rates? Maybe. Abortion rates? No. The average abortion rate for Obama's best five states is three times that of his worst five states.

http://www.thepublicdiscourse.com/2010/04/1250/

The trend is there if you look at state of residence as well (ie accounting for women that travel out of state to have abortions).

http://fivethirtyeight.com/features/pro-life-states-have-lower-abortion/

Guest said...

The treatment group consisted of women (many of them post-abortive) dissatisfied with their current birth control method. The result of the study was essentially that, if you persuade women to get IUDs, they will have fewer unintened pregnancies and fewer abortions. Given that pelvic exams are invasive enough to dissauade women from seeking birth control, I think trying to sell the IUD (a 4cm object inserted directly into the womb) to the general population would be a herculean task.

The study did not show that handing out more free contraception is the key to reducing the abortion rate, or that contraception is too inexpensive or inaccessible.

Guest said...

Good post. It's frustrating when pro-lifers dismiss contraception on the grounds that it hasn't eliminated all of the abortions. It's just as fallacious as when pro-choicers dismiss abortion bans on the grounds that they won't stop all abortions from happening. Of course they won't, but if they prevent at least one then it's worth supporting (unless there are other good reasons for being against it).

Jane Doe said...

There's another point "pro-choicers" and "pro-lifers" in favor of contraception should inform people about: how effective certain contraception-options really are and why doubling up is often a good idea.

Take for example a contraception-method which has a Pearl-Index of 99%. Sounds great, huh? Well, of course, your every-year-risk of an unintended pregnancy is only 1%, but, statistically, your risk to have a failure during the next ten years is as high as 10%! So even if you diligently use your 99%-method, your lifetime-risk (I took 30 fertile years) to have an "oopsie" is 30%. I don't think that's good enough if you're determined to stay permanently childfree.

Now, if you combine your 99%-method (like the BC-pill) with a 95%-method (like the condom) your risk to have an accident in ten years drops to 0,5% or 1,5% in 30 years. Big difference!

lady_black said...

One pregnancy will quickly disabuse any woman of the "invasiveness" of a pelvic exam. In short, the avoidance of contraception in order to avoid pelvic exams is a thought that would only occur to a man or an extremely ignorant woman, because as a method of examination avoidance, it fails BIG TIME. Which are you? A man or an extremely ignorant woman? There are few things more invasive than pregnancy. A pregnancy affects every aspect of your present and future life, health and happiness for better or worse. A pelvic exam, while not comfortable, is a mere trifle. I say keep pushing the IUDs. The avoidance of the temporary discomfort involved in having one inserted is miniscule compared to the alternative.

lady_black said...

Yes.

fiona64 said...

The Witherspoon Institute? BWAHAHAHAHAHAHAHA!

lady_black said...

What about the women who do NOT leave the state to have abortions and obtain misoprostal and have "miscarriage management" which is a euphemism for induced abortion started by a layman and completed by a doctor (or many times, simply completed by the layman. Not all, or even most medication induced abortions require medical intervention.) This occurs particularly in Texas, due to the size of the state, the proximity to Mexico, where misoprostal is available at any pharmacy just by asking, and dwindling access to safe, legal abortions. The alternative to safe, legal abortion isn't birth. It's unsafe, illegal abortion and methods that skirt the edge of that definition, like flea-market abortion pills. Laws don't work in this sphere. THEY NEVER WORKED. When laws invade medical and personal, intimate privacy, they are routinely ignored.

Guest said...

It beats Cosmo magazine, and the data is easily available on Guttmacher's website if you want to look it up yourself.

Guest said...

I go with the data. You're free to speculate about how many women are running around having these cytotec abortions, but you'll need some actual numbers to prove that abortion rates are highest in the Bible Belt.

Guest said...

You can go ahead. But family planning clinics themselves consider the pelvic exam a "major barrier" to birth control access. But what do they know? They're just men and extremely ignorant women.

http://healthland.time.com/2010/12/06/why-annual-exams-shouldnt-be-required-to-get-birth-control-pills/

fiona64 said...

You're funny. You're the one who made the positive assertion; YOU provide the citation.

lady_black said...

That article doesn't say what you think it says. The article is questioning the need for pelvic exam prior to prescribing oral contraceptives, and I agree. Nowhere does it state that it's "a major barrier" just unnecessary for the pill. You'll need to try harder than that.

Guest said...

First paragraph, second sentence: "according to a consortium of health-care providers and researchers,
called Oral Contraceptives Over-the-Counter Working Group (OC-OTC), the
annual pelvic exam is still a major barrier to access to contraception
for many American women.

Guest said...

Guttmacher is smart enough not to directly say that the average abortion rate for Obama's best five states is three times that of his worst five states. But the numbers are there.

Obama's best five states were DC, Hawaii, Vermont, Rhode Island, and New York. His worst five were Utah, Wyoming, Oklahoma, Idaho, and West Virginia:

http://www.washingtonpost.com/wp-srv/special/politics/obama-better-or-worse/

The respective abortion rates are 28.5, 21.1, 11.7, 19.8, and 34.2 for the blue states. For the reds, they're 5.4, 1.1, 7.9, 5.4, and 7. The national abortion rate is 16.9, FYI.

http://www.guttmacher.org/pubs/journals/psrh.46e0414.pdf

So if we take a crude mean, we get 23.06 for the blue states and 5.36 for the red states:

https://www.google.ca/?gws_rd=ssl#q=%2828.5+%2B+21.1+%2B+11.7+%2B+19.8+%2B+34.2%29+%2F+5

https://www.google.ca/?gws_rd=ssl#q=%285.4+%2B+1.1+%2B+7.9+%2B+5.4+%2B+7%29+%2F+5

Then we do that gazinta thing and, lo and behold, the average abortion rate for Obama's best five states is well over three times that of his worst five states.

https://www.google.ca/?gws_rd=ssl#q=23.06+%2F+5.36

(we could do a weighted average based on population if you like, though I think the same point would apply).

fiona64 said...

Only an idiot would claim that access to a full range of health services for all women is somehow bad. ::shrug:: Draw your own conclusions about how I view you, "guest."

Plum Dumpling said...

Or you could have a nice safe legal medical abortion.
All contraception has a failure rate including vasectomy.

Plum Dumpling said...

Illegal abortion is one of the three leading causes of maternal death worldwide. You are not pro life. You are pro forced birth.

Plum Dumpling said...

Poverty is the major barrier to getting an annual pelvic exam. Please.

Plum Dumpling said...

Obama owns states and wombs? Kool.

Jane Doe said...

If we told people honestly how effective one method of contraception is compared to a combination of two, I believe many, many people would opt to use two methods instead of having "a nice safe legal medical abortion". I think most people don't want to be in a situation where they have to choose what to do with an unintended pregnancy but they are because they thought they were "safe" (a doctor mocked me for using more than only the pill, because he deemed it unnecessary. And don't even try to get a copper IUD and hormonol BC... ).

All I want is that sex ed should tell what the failure rate of a chosen method really means, then let people decide. If you take the BC-bill and make a mistake here and there (wikipedia currently cites the failure rate for typical use with 9%) and you are aware that this means statistically a failure rate of 90% (!) during the next ten years I'm fine with it. In this case you made an informed choice.

Plum Dumpling said...

I am all for being informed and giving accurate information about sex and pregnancy. I have no quarrel with that.

Plum Dumpling said...

None of this has meaning for poor women, addicted women, and/or crazy women. It is nice, it is middle class, it is sensible, it is factual. So what? I speak as a woman who has had lots of experience with poverty, addiction and mental illness.
Contraception and abortion must remain safe, legal and it should IMO be easily available if not free of charge.

Bern Baiken said...

Sooo. Outlawing legal abortion would appear to be promoting illegal abortion by your logic. Then is outlawing drunk driving promoting high speed chases in which drivers and others are killed. After all, one could argue that some drunk drivers would not get into high speed chases with police if drunk driving were not illegal; thus resulting in fewer deaths from high speed chases. If we changed the law to having cops drive drunk drivers home and having someone drive their cars home for them maybe it would reduce drunk driving fatalities. Not sure that's such a bad idea actually -- kind of ambivalent about that. The difference with that and current abortion methods is that one objective of lethal pregnancy termination is to kill the unborn baby as well as free the woman from forced birth. Before I sound too hostile I would ask if you would not be so hostile to human rights for the unborn if medical science develops nonlethal methods for terminating unwanted pregnancies and allows women to chose those methods. That and promoting vasectomies rather than abortion would far better protect women's health, including physical and emotional health, IMHO. As for saying someone can't be really pro-life because illegal abortion is one of the 3 leading causes of maternal death, I would think one would need to demonstrate that illegal abortions are as likely to kill a mother as an abortion is to kill an unborn baby to support such an opinion.

eroteme said...

The purpose of abortion is to end the pregnancy. Its not the woman's fault that the embryo cannot survive without the use of her organs.

Plum Dumpling said...

"Sooo. Outlawing legal abortion would appear to be promoting illegal abortion by your logic."
//////////////////////////////
Soooo buttons. Not by my logic. By reality. Neener neener neener.
http://www.nytimes.com/2007/10/12/news/12iht-12abortion.7863868.html?_r=0

Plum Dumpling said...

These asses continually demand from women a level of compassion that exceeds their own.

Shan said...

"a doctor mocked me for using more than only the pill, because he deemed it unnecessary."

Well, that's crappy. My partner and I used 2 methods (pill/condom) for years and my doctor never said a word. If she had, it probably would have been say that since neither one of us was interested in having any more children, he should have a vasectomy. But she's not that rude.

Guest said...

The article cites "scheduling problems or resistance to seeing a doctor" as the reason why it prevents or delays women from obtaining birth control. Or reading between the lines, lots of women don't fancy having someone poke at their lady parts just to get a few pills.

Guest said...

As for saying someone can't be really pro-life because illegal abortion
is one of the 3 leading causes of maternal death, I would think one
would need to demonstrate that illegal abortions are as likely to kill a
mother as an abortion is to kill an unborn baby to support such an
opinion.


And that women are forced to have illegal abortions rather than choosing to have them.

Plum Dumpling said...

Agree. Also a reason. That is why I see some merit in over the counter birth control pills. That would be great for convenience and modesty in women and great for drug company sales. I am uneasy about having simple access to pills my prevent yearly check up. That is when you get screened for cancer, explored for tumors, tested for stds, etc. That would really not be good.

Infant rights supporter said...

Abortion is not a health service. An unborn child is not a disease; it is a human being, a separate entity from its 'container.'

eroteme said...

1) pregnancy is not a state of health. It has the potential to maim, kill and injure.

2) if a non viable embryo is a separate entity, it should be able to move out and sustain its own life without use of the woman's organs.

fiona64 said...

Abortion is a medical procedure. A zygote/embryo/fetus is not separate from the pregnant woman; you know, that whole umbilicus thing?

And the fact that you refer to a woman as a container speaks *volumes* about how sick you are.