No Birthdays Today

[Tim Spanton]

I see from the bottom of the board index that none of the 1,457 forum members has a birthday today.
Can someone of a mathematical bent, who knows how birthdays are normally distributed for a mainly English population, work out the odds of that happening?

[Jacques Parry]

I couldn't do that; but I'm wondering how the board would know when my birthday is, given that my profile doesn't say.

[NickFaulks]

First of all, have all 1457 given permission for their birthdays to be published? I don't know whether I have, although I certainly don't mind.

Subject to that, assuming all 365 dates to be equally likely ( ignoring 29/2 ) the probability of no birthdays on any given day would be exp ( -1457/365 ), so about one in 54. Should happen about seven times per annum.

I have no idea which dates are more popular than others.

[Michael Farthing]

I've always understood that Autumn birthdays are more common. These occur nine months after the dark days of Winter when there is not much to do and there is a need for warmth and companionship.., So, on that basis, revise your Mathematics Nick! [I can also confirm that there is at least one member of this forum who has not declared his/her birthday - two if we assume (not unreasonably) that Jaques is honest].

[David Sedgwick]

[I can also confirm that there is at least one member of this forum who has not declared his/her birthday - two if we assume (not unreasonably) that Jaques is honest].

There were at least three, but I have just added my date of birth to my profile.

[NickFaulks]

So, on that basis, revise your Mathematics Nick!

You haven't actually provided any data. Who do you think you are, Sir Patrick Vallance?

[Tim Spanton]

Spooky or what? The board index again shows No Birthdays Today. Now what are the odds of that happening two days in a row in autumn?

[Michael Farthing]

So, on that basis, revise your Mathematics Nick!

You haven't actually provided any data. Who do you think you are, Sir Patrick Vallance?

You think to insult me? Well , I can do much better than you, you.. Neil Ferguson!

[Joey Stewart]

Perhaps a lot of September birthdays hide that knowledge from the world as it has been a minor source of embarrament during their school years - with September birthdays you are fated to either be the oldest in the class, clearly larger then your peers and making it look like you were held back a year or more unluckily to be born early in the month and pushed forward so you are now the youngest in your year and bullied for being smaller then everyone.

[John Clarke]

..... or more unluckily to be born early in the month and pushed forward so you are now the youngest in your year and bullied for being smaller then everyone.

To say nothing of missing out on a whole extra year in what used to be called the infants (ages 5-7), and being moved up to the juniors (7-11) before you'd got your basic literacy and numerical skills bedded in. I can think of several contemporaries or near-contemporaries of mine who suffered as a result of always being that little bit behind.