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On Condom Failure

2017-07-21 · explainer · Hank · 3:56 · watch on YouTube

Topic: Health · mode: Explainer

Hank unpacks the '2% condom failure rate' he learned in sex ed: it means pregnancy per year of perfect use, not per act; the risk compounds over years (about 20% over 10 years, 1 in 3 over 20); typical use gives about 20% a year; and implants and IUDs work as well in typical as in perfect use. He wishes sex ed had taught this better.

What is said

The parts of the video and what is said in each (★ — how much it matters to the video).

00:00:00 — Topic warning: birth control and statistics

00:00:10 — The 2% failure rate from sex ed: what kind of failure, and per what?

  • ★★ In his first sex ed class Hank was told that condoms had a 2% failure rate. — 00:00:10
  • ★★★ Hank says that statistic can be misunderstood in many (about 25) ways, and sets out to explain them. (playful) — 00:00:16
  • ★★ Condoms reduce the chances of both pregnancy and disease transmission, and 'failure' could also mean a structural failure of the condom; here it means unwanted pregnancy. — 00:00:23
  • ★★ Hank used to think the 2% was per act of sex, which would be terrible: only ten times better than unprotected sex. — 00:00:45

00:00:57 — Rates are per year of use and built for policymakers; per act a condom cuts pregnancy odds about 250 times

  • ★★ Unintended pregnancy rates for birth control are given per year of use, not per act of intercourse. — 00:00:57
  • ★★★ The 2% figure means that over a year of perfect, proper condom use for vaginal sex there is a 2% chance of pregnancy. — 00:01:06
  • ★★ Per-year rates are less useful to Hank because one sexually active person may have ten times more sex than another, and is then more likely to get pregnant using only condoms. — 00:01:15
  • ★★ Such statistics are mostly meant to inform policymakers' public health decisions, not individual choices, but individuals use them as the only stats available. (hedged) — 00:01:27
  • ★★★ Per act of intercourse, using a condom cuts the odds of pregnancy about 250 times, far better than ten. (hedged) — 00:01:40
  • ★★ As far as Hank can tell, that per-act figure has never been taught in sex ed; he calculated it himself from somewhat incomplete raw data. (hedged) — 00:01:49

00:01:57 — Each year is a new roll of the dice: the risk compounds over 10 and 20 years

  • ★ Hank also misread 2% to mean two pregnancies for every hundred times. — 00:02:03
  • ★★★ The 2% chance applies anew every year: each year is a new roll of the dice. — 00:02:10
  • ★★★ Probabilities compound: over two years you multiply 0.98 by 0.98; perfect condom use for 10 years gives about a 20% chance of pregnancy, and over 20 years 1 in 3. (hedged) — 00:02:27

00:02:40 — Perfect versus typical use; implants and IUDs

  • ★★★ With typical rather than perfect use, condoms result in pregnancy in about 20% of years in which people use only condoms. (hedged) — 00:02:48
  • ★★ Typical use is how the average person uses birth control; nobody is really average, but if there's a way to mess up, people often find it. — 00:02:58
  • ★★★ Implants and IUDs, where they suit the person, have had a really substantial impact on unwanted pregnancies worldwide and in America. — 00:03:07 · United States
  • ★★★ The typical use of implants and IUDs equals their perfect use, because they always do what they are supposed to do. — 00:03:17
  • ★★ Implants and IUDs are even more effective than perfect condom use. — 00:03:23
  • ★★ Neither implants nor IUDs protect against diseases. — 00:03:26

00:03:29 — Why Hank made the video: a politicized sex-ed class, and hope for better information

  • ★★★ Hank made the video because the statistics confused him; he wishes his sex ed had been more than a basketball coach begrudgingly parroting a politicized curriculum. — 00:03:29
  • ★★ Hank hopes the internet and scientists' continuing work will let people get better information and make better decisions, even as some keep fighting to hide it. (hedged) — 00:03:41

In the description and comments

  • ★★★ The description says Hank has always thought sex ed and statistics should be one course: nothing better shows how vital statistics is to everyday life. — video description
  • ★★ The description notes a common trap: unprotected sex with no bad outcome makes it feel much safer the next time. — video description
  • ★★ Hank says a 2% chance sounds tiny but means that, on average, of 50 couples using condoms perfectly, one will get pregnant in any given year: surprising and unfair to that couple, but exactly what statistics predicts. — video description
  • ★★ Probabilities eventually collapse into reality: the couple who gets pregnant now has a 100% chance and everyone else 0%, so being one of the two percent isn't that weird. — video description
  • ★ Hank points viewers to the video on probability he made in 2010, which he is actually pretty proud of. — video description
  • ★★ Most of the video's information came from the Guttmacher Institute, which Hank praises, with its fact sheets on US contraceptive use and unintended pregnancy rates, plus a Vox article on IUDs reducing unintended pregnancies. — video description

Threads in this video

Mentioned

Central: birth control · condom · statistics · unintended pregnancy

Also: contraceptive implant · independence (probability theory) · intrauterine device · probability · sex education · sexually transmitted infection · United States

Only in the description or credits: Guttmacher Institute · risk perception · Vox

Also centred on statistics: Understanding Cancer Survival Rates

Replies to

  • continues · Probability 101 — “Here's the video I made on probability in 2010 that I'm actually pretty proud of”

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