Contraceptive failure

[pozorvlak]

This point came up in a conversation over on steerpikelet's LJ, and I thought it bore repeating here. Partly because it's important, but mostly because it allows me to talk about one of my favourite bits of maths, namely probability theory

Comments

Hmmmm

[benparker]

Whilst I agree with the point you're trying to make, measuring the statistic "% of condom splitting" seems a bit pointless. The statistic used in comparing birth control methods is normally pregnancies per thousand couples per year (which I guess is also misleading, but at least easier to measure accurately

Re: Hmmmm

[half_of_monty]

Actually, now you come to mention it, the statistic I've heard before is that `condoms have a 3% failure rate' means `3% of couples using condoms for a year end up with a pregnancy'. Er, yes, that does appear to be the actual statistic

Re: Hmmmm

[pozorvlak]

OK: the site linked referred to it as a breakage rate rather than a pregnancy rate. I suppose pregnancy rate is easier to measure, even though breakage rate is also interesting from an STD point of view.

Re: Hmmmm

[andustar]

It is morning now, I am more coherent. Geek hat on:

With STIs as well as pregnancy, measuring the actual tranmission rates is more helpful than measuring condom breaks. This has been done: HIV, HPV. It would seem that condoms are actually more effective at preventing HIV transmission than they are at preventing pregnancy. Condom break figures are just estimates based on one thing or another.

Also, on lying outright (warning: may inspire more tears).

[necaris]

Tags: maths, sex
I don't know why but that strikes me as hilarious...

[pozorvlak]

This is actually the third time I've used that pair of tags. And most of my other posts with a "sex" tag have one or more science/computing tags too :-)

[azrelle]

When we are taught about contraception methods we normally get told the theoretical failure rates and then the actual failure rates. Condoms are only as reliable as the people using them, for all kinds of reasons. You can put them on wrong, buy crap ones, not leave enough of a pouch on the end, use some kind of lubricant that weakens it, not use lubricant at all.... Hence measuring their effectiveness very much depends on what endpoint you use and whether you study them in controlled circumstances or in actual use. I can't find the exact article just now, but it has been suggested that condoms are something like 70% effective against conception in actual use when used as the only method of contraception

[half_of_monty]

Thought the coil also left open the (very nasty) possibility of eptopic pregnancies - but there may be various sorts of coil; is this the one with hormones in it too?

At this point in the conversation I usually plug the injection of depo-provera, which has nasty side effects for some but is perfectly safe and healthy for many. And it stops your periods! I also think it's a similar price to the pill. However it isn't a good idea to promote it to teens because it interferes with laying down bone density (which is more or less done by the time you're 22ish).

[pozorvlak]

Indeed. Or the implant.

[azrelle]

After doing my stint in Obs & Gyn I was thoroughly put off Implanon. They go in great but getting them out is a fucker!! We had lots of young women in their 20s and 30s who ended up with scars on their arm after having to have a minor op to go in and retreive the implant. The side effects can be really nasty and unlike all the other methods it's a bit harder to stop using the implant, especially if yours is one of the ones that's got stuck.

Sure, the majority of women get on fine with Implanon. I didn't see scars from any other contraception method though.

[andustar]

Thost statistics are definitely pregnancy rates. Not all condom breaks cause pregnancies, and not all pregnancies are caused by condom breaks (semen leaking out of the bottom being another issue). I can dig out the references to the original studies if you like.

And can I thank you for injecting some sanity into that thread? I would normally, but I didn't have the stamina to get involved in it around then.

[pozorvlak]

Good knowledge, thanks :-) And no problem about the sanity - to be honest, I was extremely surprised that atreic, a maths graduate, was coming out with such obvious nonsense.

[andustar]

There was so much crap logic on that page I didn't really know where to begin. Although this and this together made me weep more than the rest combined. I suspect I've never met you, and yet I still think you will share my pain.

[pozorvlak]

vampire_kitten generally made me weep.

[lxvxjxnkie]

I'm having a really fucking pointless argument about this with user foldl on Reddit, and I came out with an even smaller number (including the likelihood of PEP failure) and he's still going. *ARRGH!*

[pozorvlak]

You have my sympathy - this post came about as a result of exactly such a pointless argument - with a mathematician, no less!

[pozorvlak]

I've just read the thread, and it's not pretty. It looks like most of the problem is over what exactly you're arguing about - you and I were sticking to the original claim that becoming a prostitute necessarily significantly increases your risk of getting HIV, and foldl's sticking to the narrow interpretation of his words - that having more sex increases your risk of getting HIV. Which, yes, with condoms that are anything less than 100% effective (and that includes usage errors - maybe you're an expert, but it's dark and you're tired or whatever - we're all human) then he's right. But so are we.

When an argument degenerates that far, as they often seem to on Reddit, I find it best to swallow my pride and walk away - not always easy to do, mind. You're both too entrenched for either of you to win, and it's not worth the hassle.

[lxvxjxnkie]

Yep I decided to leave Reddit and concentrate on advocacy with ppl who might actually listen. I just want to find out what this jerk studied - I'm guessing it's computer science. It's definitely something where they've covered some history and philosophy of science, enough to make him think prospective studies are the only valid form of research.