UKC

/ Birthday Paradox

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handofgod on 08 Mar 2018

We have a rather annoying colleague at work. He's very able but opens his mouth without thinking which usually lands him in bother.

Anyway, a new person joined our department and the annoying colleague was somewhat amazed to find out our new colleague shares the same birthday as him.

Just to set the scene; we are all middle management and have attended university so one would assume, we are reasonably intelligent... Not this guy!

I explained to this character that sharing a birthday is not that uncommon and the odds are a lot less than one would initially assume. He went on to say I was talking nonsense and that it was very uncommon 1/365...

I then sent him this https://betterexplained.com/articles/understanding-the-birthday-paradox/

To which I got radio silence.

What a nob.

Post edited at 08:48
23
Tom V - on 08 Mar 2018
In reply to handofgod:

Give him a break. As your own quoted explanation says, it's counter intuitive.

 

2
d_b on 08 Mar 2018
In reply to handofgod:

See what he makes of the monty hall problem.

skog on 08 Mar 2018
In reply to handofgod:

You're looking at it from your point of view - two people in the room with you shared a birthday, and the chance of that is higher than intuitive, as you say.

He's looking at it from his point of view - someone in the room shared a birthday with him. The chance of that is much lower. About 1-((364/365)^(number of people in room-1)), I think (my maths may be off)!

 
1
handofgod on 08 Mar 2018
In reply to Tom V:

There's history.

He's forever dropping clangers and very argumentative.

Everyone has a version of him in their work place I'm sure.

 

6
FactorXXX - on 08 Mar 2018
In reply to handofgod:

Someone I work with was born on the 15th of September.
Father Christmas came early the previous year...

1
bedspring on 08 Mar 2018
In reply to skog:

> He's looking at it from his point of view -

 

And here is the rub Handofgod can only see it from his POV. 
Is it just possible that someone in his office who shares a birthday with someone else may say "We have a rather annoying colleague at work."

 

1
Blue Straggler - on 08 Mar 2018
In reply to handofgod:

Do you stifle cross-office banter by reading facts off Wikipedia to end friendly debates?

1
john arran - on 08 Mar 2018
In reply to skog:

> He's looking at it from his point of view - someone in the room shared a birthday with him. The chance of that is much lower. About 1-((364/365)^(number of people in room-1)), I think (my maths may be off)!

Maybe even worse than that. He's looking at the chances the new person shares a birthday with him. And he's right!

Although the usual mistake I'm sure he's making here is to wait for a coincidence to happen and then to ignore all the thousands of times it hasn't happened in other circumstances when remarking on how unlikely it was to have happened in this one.

1
d_b on 08 Mar 2018
In reply to Blue Straggler:

Far better to edit wikipedia first.  Best way to guarantee a win unless the mods are on the ball.

2
Andy Gamisou - on 08 Mar 2018
In reply to handofgod:

You're lucky.  I once worked a a group of 12 of which 2 were such people.  They ended up marrying each other.  What are the chances?

 

1
Deadeye - on 09 Mar 2018
In reply to handofgod:

 

> What a nob.

Quite so.

1
Bjartur i Sumarhus on 09 Mar 2018
In reply to handofgod:

Show him a real birthday paradox by only clubbing together to buy the "nicer" colleague a card and gift on their special day

1
rj_townsend on 09 Mar 2018
In reply to handofgod:

I suspect that at this very moment your colleague is saying to his friends that he has to work with a know-it-all knob in the office as well.

krikoman - on 09 Mar 2018
Big Ger - on 09 Mar 2018
In reply to handofgod:

> Everyone has a version of him in their work place I'm sure.

There wasn't one in my office.

 

Oh, hang about....

 

idiotproof (Buxton MC) - on 09 Mar 2018
In reply to davidbeynon:

> See what he makes of the monty hall problem.

I trust all the maths and know it's true.... bit in all honesty, i still dont get it.

 

Dax H - on 09 Mar 2018
In reply to Andy Gamisou:

> You're lucky.  I once worked a a group of 12 of which 2 were such people.  They ended up marrying each other.  What are the chances?

Got a better one that that. 

My wife and my brothers wife both share the same birthday, totally random happening. 

johncoxmysteriously - on 09 Mar 2018
In reply to idiotproof (Buxton MC):

I once explained MH to a group of bridge players. The worst player had the best explanation. Well, obviously, he said. Imagine it was a hundred doors and the guy showed me 98. I wouldn’t think it was even money I picked the car first time from 100 doors, would I?

 

jcm

 

Simonfarfaraway - on 09 Mar 2018
In reply to Blue Straggler:

snigger (I suspect so  )

Timmd on 09 Mar 2018
In reply to handofgod:

I've found the best response to such people is a philosophical 'happy days' to oneself and an appreciation of life in general. They're often not going to go away, and minding them doesn't improve things.  What can you do? ;-)

Post edited at 18:54
summo on 09 Mar 2018
In reply to Big Ger:

> There wasn't one in my office.> Oh, hang about....

As they say, every course, office, team.... has one; if you can't work out who it is, it's you! 

jess13 - on 09 Mar 2018
In reply to Dax H:

Two people I know share the same birthday as me. I probably know about 50 people by name but I know these two quite well although they dont know each other.

ceri - on 09 Mar 2018
In reply to handofgod:

As a teenager I got quite concerned I had a doppelganger when a new girl joined our Guides. She was called Kerry and shared my birthday... 

wercat on 10 Mar 2018
In reply to handofgod:

I have to disagree about it being counter intuitive.   Someone asked me this riddle many years ago (I think he said 25 people in the room) and asked what the probability was and I said off the top of my head that with that many it was "probably" a case of either yes or no so 50/50.  He was surprised and told me 50/50 was right.

And yet I was at a school of 600 for 5 years (A year = 120 roughly) and during the whole course of that period no other pupil had my birthday.  (I used to check the alphabetical list at the start of each term just out of curiosity)

Post edited at 10:51
Postmanpat on 10 Mar 2018
In reply to wercat:

> And yet I was at a school of 600 for 5 years (A year = 120 roughly) and during the whole course of that period no other pupil had my birthday.  (I used to check the alphabetical list at the start of each term just out of curiosity)

>

  Blimey, what are the chances of that?!

 

wercat on 10 Mar 2018
In reply to Postmanpat:

an equally unlikely thing happened a day or two ago!  I used the rather unusual name of someone from the past to create a login to watch a channel 4 programme.  Strangely the very unusual and old fashioned christian name of that character appeared in writing as a surname and then as an actual character minutes into the drama.

 

btw the drama was somthing I missed a year or two ago, plus I have a terrible memory for names

Post edited at 12:53
birdie num num - on 10 Mar 2018
In reply to handofgod:

All the Num Num children were born on the 8th of March on account of my birthday being on the 8th June

teh_mark on 10 Mar 2018
In reply to handofgod:

As well as being that guy, you obviously haven't considered that the probability of it being your birthday that's shared is somewhat lower than the probability that any two people will share a birthday. As pointed out above.

Middle management,condescending and incorrect, who would have thought!?

lithos on 10 Mar 2018
In reply to Postmanpat:

1 - ((364/365)**(600 + 4 * 120))  or .0.948 

to have same bday as you ,  so .052 ish to not.  (or 1/20 not really a significant p)

assuming even distribution, leap years, alpha levels,  blah blah blah

I think

Post edited at 14:22
Robert Durran - on 10 Mar 2018
In reply to idiotproof (Buxton MC):

> I trust all the maths and know it's true.... bit in all honesty, i still dont get it.

Once you think about it the right way, it's almost impossible to believe you ever could have been daft enough to get it wrong!

 

1
d_b on 14 Mar 2018
In reply to Robert Durran:

The Monty Hall problem, as originally formulated, has goats behind the "wrong" doors.

Anyone who has ever been downwind of a goat would know that all they have to do to win the prize is to ignore the maths and follow their nose.

Post edited at 16:27
pebbles - on 14 Mar 2018
In reply to handofgod:

 

> Just to set the scene; we are all middle management and have attended university so one would assume, we are reasonably intelligent...

(titters into back of hand)

 

Pero - on 15 Mar 2018
In reply to wercat:

> And yet I was at a school of 600 for 5 years (A year = 120 roughly) and during the whole course of that period no other pupil had my birthday.  (I used to check the alphabetical list at the start of each term just out of curiosity)

Even if the 120 people all had different birthdays, that would cover less than a third of the days in the year, so the probability that any of them would share your birthday is less than a third.

Ah, I guess you mean the odds that 600 people fail to share your birthday. Ignoring leap years, that would be: (364/365)^600, which is approx 19%.

You need a lot of people to be almost certain that one shares your birthday.

 

 

 

 

 

 

 

Post edited at 17:03
Wiley Coyote2 - on 15 Mar 2018
In reply to handofgod:

The odds of sharing a birthday with any random stranger are 50/50. You either will or you won't. So 50/50. Simple.

Pero - on 15 Mar 2018
In reply to Wiley Coyote2:

> The odds of sharing a birthday with any random stranger are 50/50. You either will or you won't. So 50/50. Simple.


A bit like the odds of having the same name as a random stranger. You either have the same name or you haven't. So, 50% of the strangers you meet have the same name as you?

john arran - on 15 Mar 2018
In reply to Pero:

Good to know I have a 50:50 chance of winning the lottery this week; I really ought to buy a ticket then.

handofgod on 15 Mar 2018
In reply to handofgod:

22 dislikes must be some sort of record ;)

FactorXXX - on 15 Mar 2018
In reply to handofgod:

> 22 dislikes must be some sort of record ;)

Hope the Dislikers come back on the thread and reverse their decision...

Wiley Coyote2 - on 15 Mar 2018
In reply to Pero:

Or someone getting the joke. Either they will or they won't. So that's 50/50 too

iknowfear on 15 Mar 2018
In reply to handofgod:

he might be a knob, but his day was not wasted; he learned something. 

https://xkcd.com/1053/

which reminds me of the fun times where an acquaintance insisted that the seasons should be the same all over the world, and that the kiwi/Australian barbeque for christmas is just wrong, because its winter on christmas. my my my... 

DubyaJamesDubya - on 16 Mar 2018
In reply to Wiley Coyote2:

> Or someone getting the joke. Either they will or they won't. So that's 50/50 too

Based on the responses above, much less than 50%. 

DubyaJamesDubya - on 16 Mar 2018
In reply to handofgod:

> We have a rather annoying colleague at work. He's very able but opens his mouth without thinking which usually lands him in bother.

> Anyway, a new person joined our department and the annoying colleague was somewhat amazed to find out our new colleague shares the same birthday as him.

> Just to set the scene; we are all middle management and have attended university so one would assume, we are reasonably intelligent... Not this guy!

> I explained to this character that sharing a birthday is not that uncommon and the odds are a lot less than one would initially assume. He went on to say I was talking nonsense and that it was very uncommon 1/365...

> To which I got radio silence.

> What a nob.

So the purpose of this tread is to have UKC confirm that your colleague is as stupid as you think he is?


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