Stacy Trasancos has a great blog called Accepting Abundance. She's a scientist and a homemaker and a convert to the Catholic faith. She has an interesting mathematical analysis about contraception.
If you recall, the Obama Propaganda Machine has said that 98% of Catholic women have used birth control at some point and that therefore Catholic women want free birth control just like everyone else. Of course, that number is just made up. But it is an "over time" number, not a "snap-shot" number. At some point between the ages of, say, 15 and 50, a woman who has ever been Catholic might use artificial birth control at least once. Yeah, that figure might just be up there in the high 90s. But look at it. If a woman was baptized Catholic and never set foot in a Church afterward, she counts. If she was a pagan prostitute her entire adult life and became a Catholic a year before hitting menopause, she counts. If she was engaged and used a condom once with her fiance and married the guy and never used birth control ever again, she counts. How many Catholic women (or men for that matter) are sinners? 100% of course (not counting Our Lady). How many who have any relation to the name Catholic have ever, ever used any kind of birth control ever? Quite possibly a very high number.
But how many active, devout, practicing Catholic women are using birth control right now? (I mean by "right now" not this exact second, but as part of their current way of living their lives.) That is, how many practicing Catholic women are actual, current users of birth control? I think that that number will be way less than 98%. I personally doubt that it is 0%, because none of us are perfect. But it is not 98%.
The difference is the over-time/real-world picture versus a focused, snap-shot picture. Birth control advocates play both sides, depending on how it suits them.
Birth control is usually presented in an idealized, snap-shot view. Birth control pills are claimed to have a success rate at preventing pregnancy also in the high 90s, for instance, 99% of women using the pill perfectly for one year (not counting mistakes, illnesses, other drugs that reduce the pill's effectiveness, etc.) will avoid pregnancy in that year. The question is, how many real women between the ages of 15 and 50, using the pill in real life (that is, imperfectly), will get pregnant over the years they use birth control, despite using birth control at the time of pregnancy?
Stacy does the math. It's a lot like compounding interested on your credit card. Assuming the birth control manufacturer's claim of 8% of real-world women will end up pregnant in one year, more than half will end up pregnant within 10 years. During 20 years of using the pill, and some women use it that long, 81% of women will have had at least 1 pregnancy they were trying to avoid. In those 20 years, 81% of sexually active women using birth control become potential customers of abortion providers at least once. The basic failure rate is even higher for teenagers.
There's also a lively discussion going on in her combox. (Lucky lady. My wife says that God reads my blog. He hasn't commented yet, though.) Some interesting objections, some good responses. There are a lot of assumptions with the model. A particular woman's likelihood of getting pregnant will be higher or lower depending on just how active she is, since the pill has to fail to prevent ovulation at the same time as she is, umm, active.
The one thing I want to focus on in terms of ethics (because there are very many) is why an outfit like Planned Parenthood would want to offer birth control if they make WAY more money off of abortions. They are banking on that birth control failure rate. They believe that a woman who comes to them for birth control will probably be back in a few years for an abortion.
Recently, the state of Texas has been criticized for de-funding PP through Medicaid, with the charge that poor women are ending up without birth control. That is, PP is turning poor women away because PP doesn't make any money off of them. Because of course PP is all about caring for poor women and making sure they get their birth control. It's a business ordered to a profit, and they would prefer to turn a poor woman away (expecting her to somehow afford an abortion when she needs one) than to offer her services out of charity.
So why doesn't PP just stop offering birth control altogether? They are afraid that if a woman cannot get birth control, she'll do something drastic, like not have sex at all, except with a man who loves her and who will stand by her and raise their child with her. Birth control (and abortion, by the way) does that. It makes it easier for more women who do not want to get pregnant to have sex, making the pregnancies that do occur all the more unwanted because they are seen as a bad outcome of sex.
The more people engage in sex not wanting a pregnancy, the more unwanted pregnancies that will occur. You do the math. PP has.