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# How can I be sure my girlfriend is 100% girl? watch

1. (Original post by dragonzrmetal)
Your maths is a little bit dodgy, there should be about 1 intersexual in every 60 people, but the chances are 40% after 30 people, 50% of having found one after 40 people, and go up to 65% after 60 people, etc. More importantly, selection bias. A guy suspecting his girlfriend is intersexual is probably much more likely to actually be dealing with an intersexual than a randomly selected man in a relationship.

Anyway, I don't see what the problem is if she is, but it's probably something that'd have to come from her, if you're that close I don't see why she'd keep her past secret.
It's not dodgy. When you have dated 60 people, there should be 1 intersexual. But my point was hardly anyone seriously dates 60 or 120 people. I didn't make a claim on the chances of dating an intersexual when you're dating your 61st person.

How many people have 60, 40, or 30 long-term romantic partners? Let's just say this person has short LTRs, you will need to be constantly dating with almost no breaks and rather short relationships the whole time to call 30 people your boyfriends or girlfriends.

On selection bias - we don't know who this person is or how this person is like. We also don't know the girl. We know nothing to judge whether it was even remotely reasonable.
2. (Original post by cambio wechsel)
No. If salmonella is evenly distributed between brown and white eggs, a person eating only brown eggs exposes himself to precisely the same degree of risk as someone eating both, where they consume in the same quantity.
You're right. I got mixed up with LGBT stats. Sorry.
3. (Original post by Little Toy Gun)
I didn't do the mathematics but I just assumed that figure was calculated from the 1.7% number. If you date only one of the genders, your chances of meeting an intersexual is down by half.
No it's not. Think about it, if you've halved the number of intersexual people but also halved the population (by excluding one gender) then the odds remain the same...
4. (Original post by CurlyBen)
No it's not. Think about it, if you've halved the number of intersexual people but also halved the population (by excluding one gender) then the odds remain the same...
Yes, I've made a mistake. I've acknowledged it in a post above.
5. (Original post by Little Toy Gun)
I didn't do the mathematics but I just assumed that figure was calculated from the 1.7% number. If you date only one of the genders, your chances of meeting an intersexual is down by half.

But if the 11.3% figure has already taken that into account then just forget that part.
It's not that intuitive unfortunately You need to take the odds of a person not being intersex (98.3%, or 0.983), raise it to the power of the number of people entered into a relationship with, and subtract the result from one. So if you date 60 people, the chances of at least one being intersex are 1 - (0.983^60), or 64.3% to one decimal place.
6. (Original post by Little Toy Gun)
It's not dodgy. When you have dated 60 people, there should be 1 intersexual. But my point was hardly anyone seriously dates 60 or 120 people. I didn't make a claim on the chances of dating an intersexual when you're dating your 61st person.

How many people have 60, 40, or 30 long-term romantic partners? Let's just say this person has short LTRs, you will need to be constantly dating with almost no breaks and rather short relationships the whole time to call 30 people your boyfriends or girlfriends.

On selection bias - we don't know who this person is or how this person is like. We also don't know the girl. We know nothing to judge whether it was even remotely reasonable.
It is ridiculously dodgy. The "common sense" suggestion you just made is wrong. I know your maths, you did n x probability of intergender = 100%, and found that n is 60, but that means that for an average group size of 60, one member is intergender. You should have taken the probability of their not being intersex, and raise it to the power of how many partners they have had. That is basic GCSE probability. You will find that after just 10 partners, there is a 16% chance that one of them was intersexual. 5 partners gives 8%, which again, is not small. (The relationship is not linear as number of partner approaches infinity, obviously, those numbers just happen to both double.) You do not need to have had a very large number of partners as you insinuate for a reasonable chance of finding an intersex person.

So lets suggest the average person dates say, 6 people, then they have a 10% chance of encountering an intersex partner. Selection bias is very much a thing, as we can assume the OP has some genuine reason to believe their partner may be intersex, both the dodgy medical history, and whatever else they haven't told us that gave them that idea. Someone with no suspicions would not make a post asking how to find out if their girlfriend was intersex, and someone with suspicions is more likely to actually have a girlfriend who is intersex. Pretty simple - there is your selection bias. I wouldn't laugh away the possibility of the OP's girlfriend being intersex based on some shady maths, even if it isn't the most likely possibility.
7. That thread title floored me
8. (Original post by Saoirse:3)
It's not that intuitive unfortunately You need to take the odds of a person not being intersex (98.3%, or 0.983), raise it to the power of the number of people entered into a relationship with, and subtract the result from one. So if you date 60 people, the chances of at least one being intersex are 1 - (0.983^60), or 64.3% to one decimal place.
(Original post by dragonzrmetal)
It is ridiculously dodgy. The "common sense" suggestion you just made is wrong. I know your maths, you did n x probability of intergender = 100%, and found that n is 60, but that means that for an average group size of 60, one member is intergender. You should have taken the probability of their not being intersex, and raise it to the power of how many partners they have had. That is basic GCSE probability. You will find that after just 10 partners, there is a 16% chance that one of them was intersexual. 5 partners gives 8%, which again, is not small. (The relationship is not linear as number of partner approaches infinity, obviously, those numbers just happen to both double.) You do not need to have had a very large number of partners as you insinuate for a reasonable chance of finding an intersex person.

So lets suggest the average person dates say, 6 people, then they have a 10% chance of encountering an intersex partner. Selection bias is very much a thing, as we can assume the OP has some genuine reason to believe their partner may be intersex, both the dodgy medical history, and whatever else they haven't told us that gave them that idea. Someone with no suspicions would not make a post asking how to find out if their girlfriend was intersex, and someone with suspicions is more likely to actually have a girlfriend who is intersex. Pretty simple - there is your selection bias. I wouldn't laugh away the possibility of the OP's girlfriend being intersex based on some shady maths, even if it isn't the most likely possibility.
I admit maths is not my strongest subject in school but doesn't this mean it's even less likely than I thought?

I thought statistically after 60 people the possibility should be theoretically 100%. And now it's only 64.3%.

5 partners is much more reasonable than 10 (I think 6 is around the number the average person has sex with in their lifetime, not for long-term relationships), and yes 8% is not small. But still very unlikely. As I've said, normal people don't worry about their partner being secretly gay or HIV+ (both are more likely than this) so why worry about this?

I know there can be selection bias, but I'm saying we don't know anything about either of these people here. His selection bias could be caused by his previous personal experience or the news article posted instead of anything to do with this girl.
9. (Original post by Little Toy Gun)
I admit maths is not my strongest subject in school but doesn't this mean it's even less likely than I thought?

I thought statistically after 60 people the possibility should be theoretically 100%. And now it's only 64.3%.

5 partners is much more reasonable than 10 (I think 6 is around the number the average person has sex with in their lifetime, not for long-term relationships), and yes 8% is not small. But still very unlikely. As I've said, normal people don't worry about their partner being secretly gay or HIV+ (both are more likely than this) so why worry about this?

I know there can be selection bias, but I'm saying we don't know anything about either of these people here. His selection bias could be caused by his previous personal experience or the news article posted instead of anything to do with this girl.
It means it's less likely than you thought for large numbers, and much more for small numbers. Imagine if the probability was 100% for 60, that's obviously not true for any number of partners, you could very easily get a non-intersex for every partner until you run out of non-intersex people. There's no rule that after 59 non-intersex partners, some law of nature dictates that the next will be intersex. Apologies for stating the obvious, I'm hoping it might help underline why the maths is what it is - imagine a probability tree, and just draw the branch for having a non intersex partner every time.

Anyhow, he probably has good reason for worrying about it. As you said, normal people wouldn't - unless they have a good reason. News articles are not a good reason. That is the selection bias, I don't believe he wouldn't ask for no reason.
10. (Original post by dragonzrmetal)
It means it's less likely than you thought for large numbers, and much more for small numbers. Imagine if the probability was 100%, that's obviously not true, you could very easily get a non-intersex for every partner until you run out of non-intersex people.

He probably has good reason for worrying about it. As you said, normal people wouldn't - unless they have a good reason. That is the selection bias, he wouldn't ask for no reason.
He wouldn't ask for no reason. But we don't know if the reason was even related to this girl or other things that's been going on and happened in his life.

Someone who's worried about their husband being secretly gay could have their doubt purely because her best friend's husband was secretly gay or simply because it's a plot on TV. There's a news article with the 1.7% number, saying it's say common as red heads. There's a model who's just come out as intersexual. So many things are possible and I don't think we should assume it's got anything to do with this girl in particular.

What I thought was, if you have dated 60 people, you can reasonably assume one of them was intersexual. That's correct, right?

ETA: What aren't news articles a good reason? Mexicans read about the very first school shooting in Mexico (and in an American school, no less) and the entire country's schools panicked and searched for guns. You don't know the OP.
11. (Original post by Little Toy Gun)
He wouldn't ask for no reason. But we don't know if the reason was even related to this girl or other things that's been going on and happened in his life.

Someone who's worried about their husband being secretly gay could have their doubt purely because her best friend's husband was secretly gay or simply because it's a plot on TV. There's a news article with the 1.7% number, saying it's say common as red heads. There's a model who's just come out as intersexual. So many things are possible and I don't think we should assume it's got anything to do with this girl in particular.

What I thought was, if you have dated 60 people, you can reasonably assume one of them was intersexual. That's correct, right?
I don't believe they could have that doubt from something so trivial. I stand by what I said, but I also agree that if we take your assumption that there is no selection bias, then the chances are low.

Yes, although reasonably is a strong word, there's also a 40% chance none of them were intersexual.

There's a mathematics book for popular consumption called "The Drunkard's Walk" on stats and probability and other stuff, it's one of my all-time favourites, if you're interested in this sort of stuff.
12. Why aren't they a good reason? Well, just because someone is intersex wouldn't mean my girlfriend is. I expect other people to be at-least halfway as logical as I, and I don't know that any of my friends would fall for something like that. It's pretty common sense. I don't have any reason to suppose that rational human behaviour is to get scared over a news article, or that the OP is silly enough to be predisposed to do such.
13. (Original post by dragonzrmetal)
I don't believe they could have that doubt from something so trivial. I stand by what I said, but I also agree that if we take your assumption that there is no selection bias, then the chances are low.

Yes, although reasonably is a strong word, there's also a 40% chance none of them were intersexual.

There's a mathematics book for popular consumption called "The Drunkard's Walk" on stats and probability and other stuff, it's one of my all-time favourites, if you're interested in this sort of stuff.
No, I hated maths.

I disagree with the "no smoke without fire" assumption on principle, and wouldn't assume that especially when there's literally 0 information on the girl. On the other hand, he explained what intersexuals are before saying what parents usually do. If I have to bet on this, I'd bet on his coming across a documentary or something on the topic, or even more likely, attended a lecture on that topic. And in that case, there's actually "fire", only that it's not from the girl.
14. (Original post by Little Toy Gun)
I admit maths is not my strongest subject in school but doesn't this mean it's even less likely than I thought?

I thought statistically after 60 people the possibility should be theoretically 100%. And now it's only 64.3%.

5 partners is much more reasonable than 10 (I think 6 is around the number the average person has sex with in their lifetime, not for long-term relationships), and yes 8% is not small. But still very unlikely. As I've said, normal people don't worry about their partner being secretly gay or HIV+ (both are more likely than this) so why worry about this?

I know there can be selection bias, but I'm saying we don't know anything about either of these people here. His selection bias could be caused by his previous personal experience or the news article posted instead of anything to do with this girl.
Think it through logically. If you draw four cards from a standard deck, is one guaranteed to be a spade simply because the odds are one in four? What you said before (that you'd expect 1 intersex person after dating 60) implies a greater than 50% chance after 60 (so that you'd be more likely to than not) - there is of course no such thing as total certainty, and in reality you exceed a 50% chance after 40 people, lower than your calculation
15. (Original post by Saoirse:3)
Think it through logically. If you draw four cards from a standard deck, is one guaranteed to be a spade simply because the odds are one in four? What you said before (that you'd expect 1 intersex person after dating 60) implies a greater than 50% chance after 60 (so that you'd be more likely to than not) - there is of course no such thing as total certainty, and in reality you exceed a 50% chance after 40 people, lower than your calculation
You're right, and this is a very good explanation.
16. (Original post by Little Toy Gun)
No, I hated maths.

I disagree with the "no smoke without fire" assumption on principle, and wouldn't assume that especially when there's literally 0 information on the girl. On the other hand, he explained what intersexuals are before saying what parents usually do. If I have to bet on this, I'd bet on his coming across a documentary or something on the topic, or even more likely, attended a lecture on that topic. And in that case, there's actually "fire", only that it's not from the girl.
There is definitely, no shadow of a doubt, some correlation between smoke and fire - smoke raises the probability of actual fire, even if only by say, 1%. The question is just by how much, so the principle is not null. You might be right, the explanation of the intersexual business firsthand makes it seem like it's new to him, and then we have false fire. It might be more likely false fire than real fire. I wouldn't argue that she is most likely intersex, but the chance is there, and I think it's higher than the representation in the natural population due to the smoke. The only real evidence we have is a hushed over medical problem. There aren't gonna be a lot of medical problems that have to be hushed up.
17. (Original post by dragonzrmetal)
Why aren't they a good reason? Well, just because someone is intersex wouldn't mean my girlfriend is. I expect other people to be at-least halfway as logical as I, and I don't know that any of my friends would fall for something like that. It's pretty common sense. I don't have any reason to suppose that rational human behaviour is to get scared over a news article, or that the OP is silly enough to be predisposed to do such.
People get scared over one news article all the time...They don't get scared for a very long time, but they do immediately after reading it. I've given you the example from Mexico.

I can't prove this but I'd say most people would suddenly have doubts if they read about the chances of getting cancer, or in the US a GP taking money from companies to promote a drug. Or the existence of bed bugs. Or something like "your cleaner might be an illegal immigrant". Or an article on harmful substances from some dolls or toys or food.
18. (Original post by dragonzrmetal)
There is definitely, no shadow of a doubt, some correlation between smoke and fire - smoke raises the probability of actual fire, even if only by say, 1%. The question is just by how much, so the principle is not null. You might be right, the explanation of the intersexual business firsthand makes it seem like it's new to him, and then we have false fire. It might be more likely false fire than real fire. I wouldn't argue that she is most likely intersex, but the chance is there, and I think it's higher than the representation in the natural population due to the smoke. The only real evidence we have is a hushed over medical problem. There aren't gonna be a lot of medical problems that have to be hushed up.
Let's say there is fire. Is his sudden exposure to the topic (eg documentary, TV, news etc) or perhaps an unrelated personal experience (a former girlfriend being an intersexual or a friend's girlfriend is) not fire?

I just think we don't know nearly enough to even begin to judge the reasonableness of his question.
19. (Original post by Little Toy Gun)
People get scared over one news article all the time...They don't get scared for a very long time, but they do immediately after reading it. I've given you the example from Mexico.

I can't prove this but I'd say most people would suddenly have doubts if they read about the chances of getting cancer, or in the US a GP taking money from companies to promote a drug. Or the existence of bed bugs. Or something like "your cleaner might be an illegal immigrant". Or an article on harmful substances from some dolls or toys or food.
Mexicans are Mexicans. And again, we have another bias, I'm not sure what it's called, but just because one news article shows Mexicans getting upset over news, doesn't mean people always over-react to shock news, but one incident is being overly considered.

I still disagree. This is the internet age. Someone that lets an article scare them would be at the very bottom of the IQ bell curve, and I have no reason to suppose the OP is one of them. I don't know anyone like that.
20. (Original post by Little Toy Gun)
Let's say there is fire. Is his sudden exposure to the topic (eg documentary, TV, news etc) or perhaps an unrelated personal experience (a former girlfriend being an intersexual or a friend's girlfriend is) not fire?

I just think we don't know nearly enough to even begin to judge the reasonableness of his question.
Yes, but that doesn't matter. All it means is that it's quite possible he's most likely mistaken - smoke would still increase the chance that she is intersex against that of a random selection from the natural population. (Not make it the most likely probability.) The fact is, having a girlfriend who is intersex, ie, you see her balls hanging out, is going to increase the likelihood of smoke hiding fire, and therefore there is always a positive correlation between the smoke and an actual intersex girlfriend, as statistically over a large number of people, there is no reason for people with actual intersex girlfriends to be less suspicious.

Yes, we don't have much evidence, and we can't be very precise mathematically either, but all I'm saying is I don't consider it reasonable to assume he's wrong as a result.

I'm going to sleep now anyhow, I hope we're settled now, either way, I think we both understand and hopefully respect the reasoning behind each-other's viewpoints.

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