The Birthday Paradox
Discussion
According to the birthday paradox, to have a 50:50 chance of at least two people sharing the same birthday you only need to have 23 people in the room.
There seems to be something wrong with this paradox because if there really were a 50% chance of people sharing the same birthday then - taking schools as an example - every other classroom would have at least two people sharing a birthday. From my experience that doesn’t seem to be the case. I could have been unlucky with my school but for the 50:50 to hold then across the country it must be valid. Anyone on here been in a school where half the classes have people sharing birthdays?
There seems to be something wrong with this paradox because if there really were a 50% chance of people sharing the same birthday then - taking schools as an example - every other classroom would have at least two people sharing a birthday. From my experience that doesn’t seem to be the case. I could have been unlucky with my school but for the 50:50 to hold then across the country it must be valid. Anyone on here been in a school where half the classes have people sharing birthdays?
https://en.wikipedia.org/wiki/Birthday_problem
Yes, the maths does work and does make sense.
Your point on classrooms is interesting as the maths does say that more than half of the classes in the country should have 2 kids with the same birthday and that 'feels' wrong.
I think all that is happening here is that your brain is using the counter intuitive belief to try and make your personal experience fit where in actual fact, neither you nor I have the data to say whether this is true or not and probably if we asked 100 classes of >23 kids, more than half of them would actually have a shared birthday..
Yes, the maths does work and does make sense.
Your point on classrooms is interesting as the maths does say that more than half of the classes in the country should have 2 kids with the same birthday and that 'feels' wrong.
I think all that is happening here is that your brain is using the counter intuitive belief to try and make your personal experience fit where in actual fact, neither you nor I have the data to say whether this is true or not and probably if we asked 100 classes of >23 kids, more than half of them would actually have a shared birthday..
RMDB9 said:
Just because there is a 50/50 "chance" it does not mean that is needs to happen. See Roulette.
Not sure what you mean. If you toss a coin the chance of getting heads is 50%. Of course that doesn’t mean if you toss it twice you will definitely get a heads. You could toss it ten times and get tails every time. However if you toss is a thousand times you would find that the split between heads and tails would be close to 50%. Toss it a million times and it would be very close to 50%. Same with the birthday paradox. Chose ten classes at random and it wouldn’t be 50% of classes where at least two people share a birthday. However across the whole of the U.K. it should be close to 50%.
People are posting random cases but for it to hold it really should be every other class that has people sharing birthdays.
Esceptico said:
RMDB9 said:
Just because there is a 50/50 "chance" it does not mean that is needs to happen. See Roulette.
Not sure what you mean. If you toss a coin the chance of getting heads is 50%. Of course that doesn’t mean if you toss it twice you will definitely get a heads. You could toss it ten times and get tails every time. However if you toss is a thousand times you would find that the split between heads and tails would be close to 50%. Toss it a million times and it would be very close to 50%. Same with the birthday paradox. Chose ten classes at random and it wouldn’t be 50% of classes where at least two people share a birthday. However across the whole of the U.K. it should be close to 50%.
People are posting random cases but for it to hold it really should be every other class that has people sharing birthdays.
My wife and I have the same birthday - different years, but the same day. It’s a pain the arse. We have a deal that if one of us has a milestone, the other steps back. She was 30 2 years ago, me and her sister threw her a party. I’m 30 this year so I’ll be in the spotlight. Non milestones we are better at sharing. We always do something for “our” birthday - whether that’s going away for a weekend or whatever
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