Same birthday as you?
A friend recently took a ‘quiz’ on Facebook called ‘How common is your birthday?’ It turns out this is a classic math problem. This particular friend’s result to the quiz was 6% (though the sample size was not listed). From wikipedia (see Same birthday as you): “The probability q(n) that someone in a room of n other people has the same birthday as a particular person (for example, you), is given by q(n)=1-((365-1)/365)^n. Substituting n = 23 gives about 6.1%, which is less than 1 chance in 16.” Which might mean that 23 other people have used that app in some given pool of people (his friends? his friends using the app? everybody using the app?) that the programmer chose. “For a greater than 50% chance that one person in a roomful of n people has the same birthday as you, n would need to be at least 253.” Teachers love this one in college in big lecture halls that might hold as many as 300 kids when they’re doing probability theory because folks intuitively think that in a group of 300 the chance of someone else having their same birthday is going to be near 1, but as it turns out it’s higher than 50%! The teacher can pick anyone and there’s a better than half a chance somebody else has that birthday too.
We’ll leave aside my thought that the app is just a thinly cloaked method of getting people to reveal their real birthday (and I assume check it against the one users claim in their profile)? The more of these Facebook apps I see the more suspicious I get.
Comment posted on 6-11-2009
I’ve heard from reliable sources that the guys who fly the little black helicopters use facebook too…
Comment posted on 6-11-2009
I have it on good authority that Scott would know.
Comment posted on 6-11-2009
LMAO…When do I get to throw on some leather armor and do battle?… (after I lose about 50lbs…hahaha)
Comment posted on 6-25-2009
But the quiz result says (for one of my friends), “Your Birthday is 11% Common” I don’t see any other way to interpret this other than it says that 11% of the people in the world were born on that one day. Adding in the 6% for your friend, and we have 17% of the people in the world being born on only two different dates in the year.
Does that make sense?