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Do men or women have more brothers?

math.stackexchange.com

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Re: Do men or women have more brothers?

#11

Post by dhimes »

micheljansen wrote: post #7
mudbungie wrote: post #2

I chose to answer the question empirically. http://pastebin.com/1g1bAEPt Turns out it's equal.

While that's a nice way to approach a mathematical problem, it does not take into account the social aspects of the problem. For example, it used to be (and perhaps still is?) quite common for families to aspire to have a boy and therefore have another child when they have a girl, but not when they have a boy. Interestingly, these sort of things are much easier to model empirically the way you did (all you would need…

Well, it was posted in probability and not is some social science board. So I thought it was safe to assume a purely mathematical question. Not that I can answer it...

Re: Do men or women have more brothers?

#12

Post by tomp »

paulmd wrote: post #5

Seems like a straightforward Gambler's Fallacy situation. Assuming the chances of each sex are independent and equally probable, then each subsequent child has a 50% chance of each sex. Your previous streak is irrelevant (it doesn't matter whether you're male or female), the chance of having a brother is equal. As the number of families approaches infinity the number of brothers will even out. Or to rephrase the ques…

Hm... I'm not sure you're answering the correct question.

Assume you're a man and you have a sister. Your next sibling is about to be born.

There is a 50% chance that it's a boy! In which case, he will have one brother (you), you will have one brother (him), and your sister will have 2 brothers. She wins.

There is a 50% chance that it's a girl! In which case, both she and your other sister will both have 1 brother (you), whereas you won't have any. You loose again!

Re: Do men or women have more brothers?

#13

Post by ewjordan »

tomp wrote: post #12
paulmd wrote: post #5

Seems like a straightforward Gambler's Fallacy situation. Assuming the chances of each sex are independent and equally probable, then each subsequent child has a 50% chance of each sex. Your previous streak is irrelevant (it doesn't matter whether you're male or female), the chance of having a brother is equal. As the number of families approaches infinity the number of brothers will even out. Or to rephrase the ques…

Hm... I'm not sure you're answering the correct question. Assume you're a man and you have a sister. Your next sibling is about to be born. There is a 50% chance that it's a boy! In which case, he will have one brother (you), you will have one brother (him), and your sister will have 2 brothers. She wins. There is a 50% chance that it's a girl! In which case, both she and your other sister will both have 1 brother (y…

"Assume you're a man and you have a sister."

You just put your finger on the scale. All you can assume is that you're a man, not that you have a sister.

Re: Do men or women have more brothers?

#14

Post by sp332 »

mudbungie wrote: post #2

I chose to answer the question empirically. http://pastebin.com/1g1bAEPt Turns out it's equal.

I think you forgot to put quotes around "Girl" on line 46. Edit: Actually I'm not sure what the problem is but I'm getting 0 girls and a divide-by-0 error.

Edit2: I don't remember why I was getting all girls, but the other issue was integer division. If boybrothers/boys truncates to 0, then (girlbrothers/girls)/(boybrothers/boys) will divide by 0.

Re: Do men or women have more brothers?

#16

Post by hinkley »

serge2k wrote: post #3

Classic stack overflow, top answer is a giant mass of "look how awesome I am!" sensible answer is 3 down with half as many upvotes.

That's one of my productivity secrets. Always read the top 4 answers before deciding on a course.

Answer #3 is right far too often for my liking. And sometimes answer #4 brings up corner cases the others missed.

Re: Do men or women have more brothers?

#17

Post by squidfood »

jakobegger wrote: post #6
paulmd wrote: post #5

Seems like a straightforward Gambler's Fallacy situation. Assuming the chances of each sex are independent and equally probable, then each subsequent child has a 50% chance of each sex. Your previous streak is irrelevant (it doesn't matter whether you're male or female), the chance of having a brother is equal. As the number of families approaches infinity the number of brothers will even out. Or to rephrase the ques…

Many people really want either a son or a daughter. So they'll keep trying until it works. An acquaintance of mine had four sons before the fifth one finally was a daughter. I'm pretty sure that effect is a lot stronger than any genetic predispositions.

Actually, if everyone has babies of sex A until you have a baby of sex B, you get a 50/50 mix.

  - Half the parents will have an only child of sex B.
  - One quarter will have one A, one B.
  - One eighth will have A, A, B.
  - One sixteenth A,A,A,B.
This converges on 50/50!

Re: Do men or women have more brothers?

#18

Post by boojumsnark »

jakobegger wrote: post #6
paulmd wrote: post #5

Seems like a straightforward Gambler's Fallacy situation. Assuming the chances of each sex are independent and equally probable, then each subsequent child has a 50% chance of each sex. Your previous streak is irrelevant (it doesn't matter whether you're male or female), the chance of having a brother is equal. As the number of families approaches infinity the number of brothers will even out. Or to rephrase the ques…

Many people really want either a son or a daughter. So they'll keep trying until it works. An acquaintance of mine had four sons before the fifth one finally was a daughter. I'm pretty sure that effect is a lot stronger than any genetic predispositions.

If you kept flipping coins until you got heads - would you then beat the casino on average?

Re: Do men or women have more brothers?

#19

Post by oh_sigh »

micheljansen wrote: post #7
mudbungie wrote: post #2

I chose to answer the question empirically. http://pastebin.com/1g1bAEPt Turns out it's equal.

While that's a nice way to approach a mathematical problem, it does not take into account the social aspects of the problem. For example, it used to be (and perhaps still is?) quite common for families to aspire to have a boy and therefore have another child when they have a girl, but not when they have a boy. Interestingly, these sort of things are much easier to model empirically the way you did (all you would need…

Social and biological aspects. Assume there may be some genetic factor which makes it impossible(or even just less equal-odds) for a pair to produce a female, or male. If that's the case, men will on average have more brothers than women do.

Re: Do men or women have more brothers?

#20

Post by oh_sigh »

serge2k wrote: post #3

Classic stack overflow, top answer is a giant mass of "look how awesome I am!" sensible answer is 3 down with half as many upvotes.

And of course, the "look how awesome I am" answer isn't useful at all, because there are unproven assertions made to make the question tractable, and unknown realities not brought into the problem space(for example, people having genetic predispositions towards birthing sons rather than daughters, or vice versa)
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