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).
How would you measure condom split rate? You could ask people randomly on the street (but who actually keeps records?), but I can't imagine you getting 1000 couples together and running an experiment (I would love to see the ethics board approve that one). Or you could do a simulated machine pumping test. Also, sometimes condoms do split but nobody notices- which is the most dangerous part!
Presumably independence doesn't quite work in the way you describe. There are some people who are good with condoms. There are some that are bad. (There are some that remember to take their pills. Some that don't.) More 15 year olds will probably have problems with condoms than 25 year olds. So because of that, the condom failure rate over a year is almost certain for some, and almost zero for others, certainly if you discard pre-use splittage. Also, if one does split, you're more careful next time so...
Anyway, yes, I think the main point is that it's a silly thing to measure, as you can't get good data, and to look at it on a case by case basis is misleading, as people in general have nookie more than once a year, and that's what you're actually concerned with.
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
Well, OK, and you're quite right about the idependence issue. I wasn't trying to produce a 100% accurate mathematical model of condom use, more to point out the huge difference between the two similar-sounding statistics, both as a lesson in applied probability and as a defence against evil lying bastards who want to stop condom distribution programmes. The site I linked to seemed fairly clear that it was a rate of breakage rather than a rate of conception (I'd imagined they'd recruited a thousand couples, and asked them to record if they had a condom break in a given year, thus neatly solving the "what is the average amount of sex to have in a year" conundrum), but I'm prepared to be corrected on this point.
Tags: maths, sex
I don't know why but that strikes me as hilarious...
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 :-)
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.
Similarly while The Pill is reported to be 98% effective in reality the end-users aren't anywhere near strict enough in administering it to achieve this figure. I can't remember what the actual use value is but it was somewhere around 85%.
The most effective contraceptive is the Mirena coil at 99.5%, a form of IUD, as you can do very little to interfere with its functioning short of removing it. The reported failures were also in very specific circumstances, one of which I believe was a woman who had 2 wombs and it hadn't been diagnosed before insertion. Unfortunately it doesnt offer anything in the way of protection against STDs and pelvic infections which still remains the only benefit of using condoms. It has been suggested that its use should be promoted more than The Pill due to its effectiveness and low side effect profile, but funnily enough guess which is cheaper to give out on a large scale?
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).
Interesting stuff! My point about the difference between per-year and per-use failure rates still stands, but now the numbers are rather different :-(
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.
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.
There was so much crap logic on that page I didn't really know where to begin. Although 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.
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!*
You have my sympathy - this post came about as a result of exactly such a pointless argument - with a mathematician, no less!
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.
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.