Facebook and the birthday paradox
This is one for math geeks with a Facebook account. I recently heard of an interesting probability problem called the Birthday Paradox. I think it was on the excellent Five Numbers series on BBC Radio 4 (or one of the 2 follow-up series). Anyway, the problem states that if you put 23 (or more) randomly selected people in a room, there is more than a 50% chance that at least 2 people will share the same birthday. The solution is not a paradox in the logical sense, it just contradicts our intuition.
Now for the Facebook link. If you have an account you probably know about the birthdays page where you can see a list of all your friends’ birthdays. I checked it the other day and was surprised to find that 3 pairs of my friends shared the same birthday. That is, before I remembered the birthday paradox and that with my 40 Facebook friends there is a 90% chance that at least 2 of them share the same birthday.
If, unlike me, you are uber popular on Facebook and have more than 100 friends, the probability should be more than 99.99996%!
(OK, I did say that this one was for math geeks…)
January 22nd, 2008 at 8:51 am
Oops, seems I didn’t understand the paradox at first read.
It says that any two people will share a birthday, not that I would share it. So then my situation (2 matches) is completely normal.
I don’t feel special anymore
haha
January 22nd, 2008 at 8:48 am
Sorry, I have 67 friends and no match… seems 9 months before 12 February is not a popular date for hooking up!
And oddly enough, between all of my 67 friends, there are only 2 matches.
Are you sure the paradox is right?
(I know it’s right, just my case is a special one).
December 18th, 2007 at 11:27 pm
I had heard about this before, but never knew the numbers… it’s amazing. It is really so counter-intuitive.
So the numbers, are they based on straight probabilities, or observations?
@pete 7 pairs… out of how many friends?
@lily Nov 10
December 14th, 2007 at 11:14 am
@martin - overstate - never this blog *is* certainly more popular than facebook..
@lilly - 11/05
December 14th, 2007 at 11:08 am
@lily: I think you’re overestimating the popularity of my blog ;-). The paradox thing will start working when 23+ people post their birthday. As far as I know, we are only 5…
December 14th, 2007 at 1:36 am
i m so angry
i m so bored
i m so crazy
i m so wacky
i m so tackky
lol this is fun no1 will probaly ever read this
December 9th, 2007 at 12:27 am
No buddy comes on no more this is becoming stupid i feel like i m talking to myself