Now What would be the odds?

[JohnB]

I was just looking at the bottom of the index page, who is on and the like when I noticed;

0 member(s) have a birthday today

No members are celebrating a birthday today

 

With 21,310 members, what are the odds? I really thought that we would have at least 1 member having a birthday every day.

[timo]

Was that question serious? The probability is roughly [math]\left(\frac{355}{356}\right)^{21310} = 10^{-26} = 0[/math], of course.

[Sisyphus]

It shouldn't be out of 21310, but out of however many members list their birthdays in their profiles. (SFN has no power to automatically deduce when you were born.) I would expect no more than a few hundred.

[timo]

Right.

[swansont]

It's also not necessarily a matter of the probability of that being true today, in particular, but of there being some day in the year without a birthday. If we had fewer than 365 registered members (cruelly ignoring those born on Feb 29 of a Leap Year), then the probability is 1. So the form of equation can't be quite right, if that's how the question is interpreted.

[Cap'n Refsmmat]

The probability is also dependent on whether my disabling the Calendar module also turns off the birthday display.

 

Hmm.

[John Cuthber]

The probability of that message being displayed is 1; it happened.

[Cap'n Refsmmat]

The probability is also dependent on whether my disabling the Calendar module also turns off the birthday display.

 

Hmm.

 

So it turns out the probability of there being no birthdays is 1 when I disable the Calendar feature.

 

Now you can calculate the odds of there being ten birthdays today...

[JohnB]

Well, that will learn me to ask a rhetorical probability question in a room full of scientists, won't it?

 

I just thought it unusual.

Edited July 17, 2010 by JohnB