“Just say no”: Does chastity work?


The recent amazing discovery that teens like sex has led to campaigns promoting chastity among high school students. Advocates for this crusade condemn the promotion of condom use, claiming that avoidance of sex is the only way to prevent unwanted pregnancies and sexually transmitted disease.

They are right, of course. Condoms sometimes fail. But there is a difference between pledging to abstain from sex and actually doing so.

Somewhere in the medical school curriculum, students learn the difference between effectiveness and efficacy. Efficacy is not just a fancy word for effectiveness. The efficacy of a treatment is a measure of how well that treatment works when applied diligently. The effectiveness of a treatment is how well it works in the real world.

Suppose a carefully constructed clinical trial of a medication for hypertension (high blood pressure) shows that the medication reduces blood pressure in 90 per cent of the subjects who got it. Since clinical trials are well-supervised and subjects tend to be compliant, that 90 per cent is a measure of the treatment’s efficacy.

When a working physician actually prescribes the drug, however, compliance is never perfect. Patients may fail to fill the prescription, they may forget to take the drug or they may stop taking it before the treatment period ends. The drug “works” for, say, only 50 per cent of patients. That’s the effectiveness of the treatment.

So while the efficacy of pledging chastity in preventing pregnancy is 100 per cent, its effectiveness is likely much less. I have heard that chastity programs are about as effective as programs that tell teens about condoms, but I can’t cite a source for that.

“Sure, kid, pledge for chastity. But, just in case, here’s a pack on condoms.”

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About aharmlessdrudge

Way back during the late Bronze age -- actually it was the 1950s -- all of us in high school had to take a vocational test to determine our interests and, supposedly, our future careers. I cannot remember the outcome, but I do recall one question that gave me pause. "If you were to win a Nobel prize, would it be in literature or in physics?" I hesitated over the question: although I enjoyed mathematics and science more than English class, I did have a couple of unfinished (and very bad) novels hidden away at home. I cannot remember what I chose back then, but the dilemma followed me to university, where I switched from mathematics to English and -- after a five-year stint in journalism -- back to mathematics. I recently retired as a professor of statistics. Retirement. What a good chance to revive my literary ambitions. I have finished a novel -- more about that in good time -- and a rubble of drafts of articles about mathematics and statistics is taking up space on my hard disk.
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