melrich Posted January 30, 2008 Share Posted January 30, 2008 In other words, it is 40 pregnancies out of 2,000 in that 20 years. Yes but that logic seems beyond everyone. I don't know why they keep thinking it is static sample of 100 women either. I also don't know why they keep using 2%. That is user failure rate, not contraception failure rate. Link to comment
RayKay Posted January 30, 2008 Share Posted January 30, 2008 Well, the "typical user failure" rate is 5% - meaning real world conditions with real people. The "lowest" failure rate (which would be lab-created use...the manufacturers use those stats in their advertising) is less than 1%. Most real world experience would fall in between these. Link to comment
rocio Posted January 30, 2008 Share Posted January 30, 2008 Look I know you guys want to reach through the computer and strangle me right now. thank you RayKay for trying to help me understand this. I have 2 problems with your conclusions: 1. The women in your hypothetical study only participate for 1 year. It doesn't matter if the sample size is 2 or 2 million, they are only participating for 1 year. What I'm trying to figure out is for the same woman who is sexually active for 20 years. (Imagine flipping a coin 100 times. What are the chances that, out of those 100 times, you will flip a head at least once?) 2. Once a woman becomes pregnant, she is not kicked out of the study. There is a period of about 1 year during which she cannot become pregnant. But after that, she's back in the study. (Women can have more than 1 child over the course of 20 years.) Link to comment
rocio Posted January 30, 2008 Share Posted January 30, 2008 I also don't know why they keep using 2%. That is user failure rate, not contraception failure rate. That's just a hypothetical value I came up with. With perfect use, it's more like 99.5-99.8%. I apologise - I just pulled the 2% from a quick google search and used it more as a hypothetical value. With an effectiveness rate of 99.8%, there would be 4 pregnancies, on average, over the course of 20 years, assuming that a woman can get pregnant while already pregnant. 4 is much lower than 40. Thank you. Link to comment
RayKay Posted January 30, 2008 Share Posted January 30, 2008 Look I know you guys want to reach through the computer and strangle me right now. thank you RayKay for trying to help me understand this. I have 2 problems with your conclusions: 1. The women in your hypothetical study only participate for 1 year. It doesn't matter if the sample size is 2 or 2 million, they are only participating for 1 year. What I'm trying to figure out is for the same woman who is sexually active for 20 years. 2. Once a woman becomes pregnant, she is not kicked out of the study. There is a period of about 1 year during which she cannot become pregnant. But after that, she's back in the study. (Women can have more than 1 child over the course of 20 years.) The data is a compilation of LOTS of data. The rates are compiled from hundreds of thousands of women, over various years, for various lengths of time. Most often, the statistics use FIRST YEAR failure rate to indicate the average for other years. If anything, after the first year, the rate should decrease as BC tends to be a bit more effective over time particularly as women are more likely to be in a routine and have found the method that works for them. For example, the copper IUD's effectiveness increases after the first few months/year. One site basically said the date can complete a sentence like this: "In 100 users who start out the year using a given method and who use it correctly and consistently, the lowest observed failure rate has been ———" "In 100 typical users who start out the year using a given method, the number of pregnancies by the end of the year will be ———" link removed And they don't reuse the same women over and over again. It just does not work that way. Over 20 years, the average failure rate would not go above the 2% (or whatever stat you are using) as it would not become "riskier" for her over time compared to the first year. Now, of course if she starts missing pills in her 5th year say, her risk will increase but that comes down to user error, not birth control effectiveness. Link to comment
rocio Posted January 30, 2008 Share Posted January 30, 2008 nevermind. we're speaking a different language here. agree to disagree? Link to comment
greenmonster Posted January 30, 2008 Share Posted January 30, 2008 I think we are all trying to add in too many outside details of the situation...and getting to micro-cosmic about it... going back to the broad picture...I think we can all agree that the correct number isn't 50% and whatever media source the OP got this number from cannot be trusted nor taken as any kind of valuable or accurate information. Link to comment
rocio Posted January 30, 2008 Share Posted January 30, 2008 Ok I know you guys are going to kill me and I hope you'll still be my friends. *blush" "An annual probability of pregnancy of 3% implies a 26% probability of pregnancy over 10 years." (My interpretation: It would be (%)x(years)=(3)x(10)=30% except for the fact that you can't get pregnant while still pregnant, so it's slightly lower.) link removed Link to comment
greenmonster Posted January 30, 2008 Share Posted January 30, 2008 Ok I know you guys are going to kill me and I hope you'll still be my friends. *blush" "An annual probability of pregnancy of 3% implies a 26% probability of pregnancy over 10 years." (My interpretation: It would be (%)x(years)=(3)x(10)=30% except for the fact that you can't get pregnant while still pregnant, so it's slightly lower.) link removed this is using straight line mathmatics which would be correct if it made sense to apply strait line math to life...but considering the time in volved that number cannot logically be used... if that was the case...then at the end of year 9 if you haven't gotten preggo then that means that durring year 9 you would have a 30% chance of becoming preggo..which isn't correct..it would still just be your 3% chance....considering that you wouldn't factor in the 3% chances from each year in the past...unless of course you have a time machine and intend on going back into the past and trying to be come preggo.. mathmatically speaking....you cannot realistically take furture %'s and past %'s and add them together when you talk about something like this because it isn't realistic. turn your numbers around and maybe this will help you make sense of it....if you think that you have 3% X 10 years = 30% of getting preggo...then wouldn't that mean you have a 97% X 10 years = 970% chance of NOT getting preggo? 970% chance....doesnt make sense right? so in theory you cannot take strait line mathmatics into this problem...97% means 97%...it doesn't mean 97% this year and 94 the next and 91 the year after...it doesn't have those kind of returns...it means 97%... or whatever other number you wanna use...the number is arbitrary hope this helps Link to comment
grendel Posted January 30, 2008 Share Posted January 30, 2008 Ok I know you guys are going to kill me and I hope you'll still be my friends. *blush" "An annual probability of pregnancy of 3% implies a 26% probability of pregnancy over 10 years." (My interpretation: It would be (%)x(years)=(3)x(10)=30% except for the fact that you can't get pregnant while still pregnant, so it's slightly lower.) link removed Congrats on finding a source for this to prove to everyone that we're not nuts... I believe the formula they used though is .97^10 (.97*.97*.97*.97*.97*.97*.97*.97*.97*.97) = 0.737 chance of *NOT* getting pregnant , or 1-0.737 = 0.263 chance of getting pregnant, or about 26%. It's not precisely a matter of addition, as we all know if you flip a coin you have a 50% chance of getting heads, but if you flip a coin twice you do not have a 100% chance of getting heads at least once. In fact you have a 0.5*0.5 = 25% chance of getting tails both times, which is equivalent to (1 - 0.5*0.5) = 75% chance of getting heads at least once. I think everyone is under the impression that you are asking a different question than you actually are... Link to comment
rocio Posted January 30, 2008 Share Posted January 30, 2008 No, you're right. It's not straight math. My point is that it's a good approximation, though. Like I said, the actual statistics of it make my head spin and I'd have to look back to my high school notes to figure out the exact formula. People are saying that your chances of getting pregnant over 10 years are 2%, if your chances of getting pregnant over 1 year are 2%. That's simply not the case. Each year, your chances of getting pregnant greatly increase (not per year, but overall). What you're saying is very similar, from what I can understand, to what I said here: "Forgetting the math and approaching it logically.. On average, 2 women out of 100 will get pregnant in a year. So, assuming you could get pregnant while already pregnant, if you did the same test over again with the same women the next year, another 2 would get pregnant. Continue the test for 5 years, and 10 women should get pregnant, on average. After 20 years, there should be 40 pregnancies, on average. But that doesn't necessarily mean that there's 40% chance of pregnancy after 20 years, because: After 50 years, there would be 100 pregnancies, on average. 100 pregnancies out of 100 women. But that doesn't mean that a woman will get pregnant with a probability of 100% because the same woman could get pregnant several times. So, the probabilities make my head hurt. But logically, after 20 years, there should be 40 pregnancies, on average. Shouldn't there? " Link to comment
rocio Posted January 30, 2008 Share Posted January 30, 2008 Congrats on finding a source for this to prove to everyone that we're not nuts... I believe the formula they used though is .97^10 (.97*.97*.97*.97*.97*.97*.97*.97*.97*.97) = 0.737 chance of *NOT* getting pregnant , or 1-0.737 = 0.263 chance of getting pregnant, or about 26%. It's not precisely a matter of addition, as we all know if you flip a coin you have a 50% chance of getting heads, but if you flip a coin twice you do not have a 100% chance of getting heads at least once. In fact you have a 0.5*0.5 = 25% chance of getting tails both times, which is equivalent to (1 - 0.5*0.5) = 75% chance of getting heads at least once. I think everyone is under the impression that you are asking a different question than you actually are... What? You're back now that I have evidence?? Where were you when I needed you.. lol.. Sorry guys. We're having a snow storm and I've hardly left the house in going on 4 days and this is about the most excitement I've had all week. I know I'm being really annoying. Please excuse me. Link to comment
melrich Posted January 30, 2008 Share Posted January 30, 2008 Congrats on finding a source for this to prove to everyone that we're not nuts... I believe the formula they used though is .97^10 (.97*.97*.97*.97*.97*.97*.97*.97*.97*.97) = 0.737 chance of *NOT* getting pregnant , or 1-0.737 = 0.263 chance of getting pregnant, or about 26%. It's not precisely a matter of addition, as we all know if you flip a coin you have a 50% chance of getting heads, but if you flip a coin twice you do not have a 100% chance of getting heads at least once. In fact you have a 0.5*0.5 = 25% chance of getting tails both times, which is equivalent to (1 - 0.5*0.5) = 75% chance of getting heads at least once. I think everyone is under the impression that you are asking a different question than you actually are... Look we are beating a dead horse here. You are seperating what the "2%" statistic is from your mathematics. If you were talking about a static group of 100 people and the chance of getting pregnant in anyone year was 2%, your maths would be a very rough approximation. An actuarial calculation would take into account the rate of infertility, the down time due to occurring pregnancies, the ageing demographic of the static group, the progressive weeding out of poor practitioners etce etc etc. BUT WE ARE NOT!!! We are talking about a RANDOM group in any one year. It is completely different. Link to comment
rocio Posted January 30, 2008 Share Posted January 30, 2008 You're right, Melrich. This doesn't take everything into account and it's not meant to be totally realistic. It's a hypothetical situation. The point was to show that something like a 98% rate of effectiveness seems really high. But when you consider it over many years, it's not really that high. That's all. There were several posters on here who thought that a BC with a 98% effective rate gave you a 2% chance of getting pregnant over a lifetime of sex. I just wanted to point out that wasn't the case. The exact figures can be calculated by the experts. Link to comment
greenmonster Posted January 30, 2008 Share Posted January 30, 2008 Congrats on finding a source for this to prove to everyone that we're not nuts... I believe the formula they used though is .97^10 (.97*.97*.97*.97*.97*.97*.97*.97*.97*.97) = 0.737 chance of *NOT* getting pregnant , or 1-0.737 = 0.263 chance of getting pregnant, or about 26%. It's not precisely a matter of addition, as we all know if you flip a coin you have a 50% chance of getting heads, but if you flip a coin twice you do not have a 100% chance of getting heads at least once. In fact you have a 0.5*0.5 = 25% chance of getting tails both times, which is equivalent to (1 - 0.5*0.5) = 75% chance of getting heads at least once. I think everyone is under the impression that you are asking a different question than you actually are... the only problem with this is that it isn't logical to apply this to the actual real world. the %'s aren't based on a single subject...they are a factor of multiple subjects... so in theory if you have 3 out of 100 women get preggo over a year then that is 3%...fine...ok..now lets move forward to 10 years...where you will have 30 preggos...30% right? no....thats 30 out of 1000 which means 3%. the equasions aren't linear and add to one another or even multiply by one another on an annual basis in a way that makes logical sense...the number that results is simply not accurate. its taking time as a relevent value when in actuality the time is constant in this equasion... 3% over a year...now does that mean that you only have a .25% chance per month? or say if you have sex 100 times in a year does that mean you have .03% chance each time? NO!!! it means you have 3% chance each time you have sex...it means you have a 3% chance each month...and since the number is constant going downward that means its also constant going forwards... there is no way to accurately factor in that 3% figure into a period of time style of equasion...the studies use years as a nice round approximation and example...not as a measuring stick.... if a woman gets preggo durring the time frame of a year...can she get more preggo 3 months into it? no...of course not...but didn't 3 months pass? how can that time be accounted for? it cant!! thats why you cannot do a calculation like this... time is constant...assume that 1 year is the same as 10 years...or a million years or 5 minutes....now do your math and you'll find that you're left with nothing but that 97% number or whatever times nothing else...becuase the thing that you were multiplying it by doesn't make logical sense to use and thus you are left with a standard variable by itself without anything to multiply it against which would then yeild the number itself... does this make sense? Link to comment
rocio Posted January 30, 2008 Share Posted January 30, 2008 so in theory if you have 3 out of 100 women get preggo over a year then that is 3%...fine...ok..now lets move forward to 10 years...where you will have 30 preggos...30% right? no....thats 30 out of 1000 which means 3%. Yes, the expected number of pregnancies after 10 years would be 30. It would be 30 pregnancies out of 1000 woman-years, not out of 1000 women. So, it would be 3% per year - not per 10 years. Link to comment
greenmonster Posted January 30, 2008 Share Posted January 30, 2008 Yes, the expected number of pregnancies after 10 years would be 30. It would be 30 pregnancies out of 1000 woman-years, not out of 1000 women. So, it would be 3% per year - not per 10 years. Now your linking the number of preggo's to the number of years...which are two entirely different things. 30 woman years out of 1000 woman years is still 3%... answer this....if Woman A has sex 300 times in Year X and Woman B has sex 3 times in Year X....who has the higher possiblity of getting preggo? by using your calculation where time is the main variable then they would have the same % chance to get preggo...does that make sense? how would you take 3% of 3 times? so like Woman B would only be able to get preggo durring the last 5 minutes of the third time? no...it doesn't work like that because its not a time based calculation...it cannot be because TIME DOESN'T MATTER...TIME IS CONSTANT. this is getting circular and I'm sory if I cannot explain it better... just understand that time is constant and it doesn't matter if its a day a week, a year, or 500 years...its the same 3%...trying to factor that 3% chance into a time style equasion isn't logical and cannot be done. getting a number as a result is a number that has nothing to with anything...its not a practical number. if there is a 5% chance that over a lifetime a human being will get cancer...does that men that you take all 6.5 billion peoples lifetimes and say that over a lifetime that theres actually a 50% chance you will contact cancer or whatever the number would end up being? NO...because its a constant 5%...much like the 3% is a constant 3% (WARNING: the previously stated information about cancer is completely made up and used as an example only...not meant to start another debate and could have used unicorns instead) Link to comment
rocio Posted January 30, 2008 Share Posted January 30, 2008 It doesn't factor in the number of times you have sex in a year. That's taken as the average over the sample. Of course, if you have sex more often than the average woman in the sample, you have greater chances of getting pregnant. If you have sex less often, you have less chance. But when they do statistics, they take an average number of times and that doesn't factor it. What you're saying is that you have a 3% chance of getting pregnant per sexual encounter, per month and per year. So, take 100 women, they all have sex once, and 3 of them will get pregnant, by your logic. Now take 100 women and let them have sex for a month, again 3 out of every hundred will get pregnant. Now take 100 women and let them have sex for a year, again 3 out of every hundred will get pregnant, on average. That doesn't make sense, does it? And if it doesn't matter how long the period of time is, then how do you reconcile the link I put up, which stated that: "An annual probability of pregnancy of 3% implies a 26% probability of pregnancy over 10 years." link removed Ok, I'm banning myself from this thread now. Link to comment
grendel Posted January 30, 2008 Share Posted January 30, 2008 I think the 2% per year fertility statistic is saying that if you're a completely average person who has a completely average level of fertility and has sex a completely average number of times per year and uses the pill with completely average regularity, then your chance of getting pregnant after a year on the pill is around 2%. Since most of us don't know if we're above or below average in these ways, we're just using the average to calculate an approximation of how likely it would be to have become pregnant at some point during 20 years. It seems a useful thing to think about since some people don't want to become pregnant this year, next year, or any time in the next 20 years. While we realize that the chances of becoming pregnant during a year are the same no matter if the year is 2008 or 2009, we are interested in the chances of a given individual becoming pregnant at some point during 20 years of sexual activity whilst on the pill. I am going to shut up about this now and also apologize if I've been annoying. Link to comment
greenmonster Posted January 30, 2008 Share Posted January 30, 2008 first off...the link doesn't work for me...dunno if its my office's firewall or filter or what....sorry... I cant explain this any clearer than this... if the concept of 26% over 10 years is accurate...if that was the case then you would mean you have a .21% chance per month...and considering that you have sex more than once a month and each time you have sex you have a 3% chance of getting preggo "in theory" then the factors of time cannot be used. becasue 3% does not equal .21% just do this....time isn't real...time is a concept that doesn't hold truth to this...dunno how I can explain it better than that...so take 97% times somethign that doesn't exist and isn't there because it doesn't apply to this and you will end up with 97%... I'm not frustrated with tryin to explain it...I just don't know any better ways to... look at Time as something constant instead of variable...which means that one year is the same as 10...or same as a month... Link to comment
toshiba Posted January 30, 2008 Share Posted January 30, 2008 I think that by the time agreement arrives on this thread, 5 million babies will have been born to women who were on birth control. Link to comment
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