Tuesday, November 27, 2007

Facebook meets the Birthday Paradox

Logging in to Facebook this morning there was a great demonstration of the Birthday Paradox (which isn't actually a paradox, it's just that people get surprised by it).

I have 95 'friends' on Facebook, and this Thursday three of them have a birthday. Wow! Or not, wow, in fact since the calculation in the birthday paradox shows us that this is very likely to happen.

Once you reach 57 friends there's a 99% likelihood that two share he same birthday, with 95 friends your getting very close to 100%. So the fact that three people have the same birthday is not at all unlikely. In fact the birthday paradox can be generalized to cover more than two birthday's being the same. My three birthday example with 95 friends would happen with probability well over 50% (which happens with 88 friends).

1 comment:

Jon G said...

Interesting. I checked the birthdays of my friends on Facebook. Out of 39, two pairs share the same birthday. Quite interestingly, none of their birthdays fall in August or November.