This discussion is now closed.

Check out other Related discussions

Thought.

Condoms are what, 99% effective? If that's the case, does that mean if you have sex 100 times using a condom then one of those times will lead to pregnancy?

Theoretically, yes

Yes. Just make sure every 100th time you do it, you use a crisp packet for extra protection.

Reply 3

Ferret_messiah

8

need_money

Condoms are what, 99% effective? If that's the case, does that mean if you have sex 100 times using a condom then one of those times will lead to pregnancy?

No, for the same reason that if you flip a coin twice you won't necessarily get a head and a tail, even though the odds are 50/50.

Reply 4

Natalie Lane

9

I think they're actually 97% :smile:

(not that it makes much difference...)

Reply 5

visesh

17

No, it means that they are not 100% reliable. You could become pregnant after 1 use, or 123242 uses, or never. But in the general population, a larger sample, about 1 in 100 uses lead to pregnancy.

Chances are, they don't say it's 100% effective to save their arses.

Reply 6

Jonny W

8

need_money

Condoms are what, 99% effective? If that's the case, does that mean if you have sex 100 times using a condom then one of those times will lead to pregnancy?

Post in the Maths forum if you really want the answer!

Reply 7

need_money

OP

9

T'isnt a maths question. T'is a health related question.

Reply 8

Jonny W

8

need_money

T'isnt a maths question. T'is a health related question.

OK, on average you will get pregnant once. But you could get pregnant any number of times from 0 to 100.

Reply 9

covered farm wagon

11

Well, it means that each time you use one, the chances of it not working are 1/100. Sounds obvious, but it also means that the chance of it happening doesn't actually increase the more you use them - each time it's still 1/100. So the chances of it not working are the same the first time you use one and the thousandth.

It's confusing though. I never went beyond GCSE maths :redface:

Reply 10

SilverWings

14

covered farm wagon

Well, it means that each time you use one, the chances of it not working are 1/100. Sounds obvious, but it also means that the chance of it happening doesn't actually increase the more you use them - each time it's still 1/100. So the chances of it not working are the same the first time you use one and the thousandth.

It's confusing though. I never went beyond GCSE maths :redface:

Each condom is a different condom... therefore they are independant events and dont affect each other... :rolleyes:

Reply 11

covered farm wagon

11

need_money

Condoms are what, 99% effective? If that's the case, does that mean if you have sex 100 times using a condom then one of those times will lead to pregnancy?

Actually, because it's late and I should be in bed, I'll be picky and point out that the 1% chance isn't of pregnancy, but of the condom failing. The chances of pregnancy are even less, because there isn't a 100% chance of getting pregnant each time you have unprotected sex.

So there :p:

Reply 12

covered farm wagon

11

SilverWings

Each condom is a different condom... therefore they are independant events and dont affect each other... :rolleyes:

Wow, you just said what I was trying to say in about a third of the space! Well done!

I find probability a bit confusing in general though. Have you read The Curious Incident? The bit about The Monty Hall Problem? I still haven't quite got my head around that one.

Reply 13

visesh

17

P(not getting pregnant) = 0.99
P(not getting pregnant after n events) = 0.99^n
P(getting pregnant after 100 uses) = 1 - 0.99^100 = 0.634 (3sf)

This is if all the events are independant, I think. I haven't done any stats in 2 years, and maths in one :p:

BUT, this is all *******s as we don't know exactly how efficient they are. HOW did they come up with that figure?

Reply 14

SilverWings

14

covered farm wagon

Wow, you just said what I was trying to say in about a third of the space! Well done!

AS Level maths :frown:

Probability :frown:

Venn Diagrams :mad:

Reply 15

need_money

OP

9

visesh

P(not getting pregnant) = 0.99
P(not getting pregnant after n events) = 0.99^n
P(getting pregnant after 100 uses) = 1 - 0.99^100 = 0.634 (3sf)

This is if all the events are independant, I think. I haven't done any stats in 2 years, and maths in one::

0.868745813 :redface:

what does that mean?

Reply 16

kingslaw

14

I'm guessing that a lot of the time, most of the accidents in that 1% were the fault of the people using the condom.

Either that, or that 1% represents the number of condoms the Catholics put holes in.

Reply 17

covered farm wagon

11

SilverWings

AS Level maths :frown:

Probability :frown:

Venn Diagrams :mad:

That sounds quite scary... I'm doing a module (philosophy degree) about classical probability and frequency and propensity theories. Actually, I have a lecture on it tomorrow morning at 9, so perhaps I should go to bed and pretend probability never happened.