Birthday greetings

[Dan Scoones]

Garry Kasparov, Konstantin Sakaev... and our own Lynn Stringer, (retired) TD extraordinaire!

[Gordon Taylor]

Re: Birthday greetings

Wow, Lynn and Garry born on the same day! It all makes sense now. :-)

Happy Birthday to all!

[Aris Marghetis]

Re: Birthday greetings

Here is a little chess-related story about birth dates that some might find interesting :

Every few months, I run a kids tournament in the suburban part of town that we live in. To make it more interesting for the returning kids, and especially those that also play in Brad's monthly CMA tournaments, I also rate mine with the CMA (like, why not, it is just so easy to SUBMIT RESULTS ONLINE, and it costs me just DIMES PER PLAYER, LOL ;)

Anyway, sidehanded dig over, all of the players rated by the CMA have an entry in the CMA database. So, if it is a kid's first tournament, I will need to enter their birthdate in the CMA database. Therefore, when the kids register, my little registration form includes a line for their birth date, in case I need it later.

Now, a few tournaments ago, I somehow ran out of those little registration forms, and was just 1 short (unless someone else showed up even later than this 1 late kid). So I grabbed the first form on the top of the already registered pile, walked over to the front desk in the building, asked for a copy of that form, then crossed out the hand-written entries on this new copy, and presented it to the father of the last kid to register, with an apology for the messy form. He said no problem, and quickly filled it in appropriately.

The tournament runs itself as expected, medals and trophies get distributed, and I head home to eat a nice hot dinner while watching NFL on TV. As the night game rolls around, I grab my laptop, and start entering the results from the tournament earlier that day.

Sure enough, that last kid was a new one, and I have to create a new entry for him in the CMA player database. Now, when I look at his form, lo and behold, this kid has the EXACT same birth date (day & month & year) as the kid whose form I had copied, and crossed out the original entries. Is that cool or what?! :)

[Egidijus Zeromskis]

Re: Birthday greetings

Is that cool or what?! :)

Have you mentioned somewhere math? :D Check the birthday problem http://en.wikipedia.org/wiki/Birthday_problem

[Aris Marghetis]

Re: Birthday greetings

Have you mentioned somewhere math? :D Check the birthday problem http://en.wikipedia.org/wiki/Birthday_problem

It seems to me though that the birthday problem you refer to is for DAY & MONTH only. In the situation that I described, it was an exact match for DAY & MONTH & YEAR. In addition, it was not a match with ANY of the other kids in the tournament, but rather a perfect match with the kid who registered immediately before him. The odds increase!

[Egidijus Zeromskis]

Re: Birthday greetings

It seems to me though that the birthday problem you refer to is for DAY & MONTH only. In the situation that I described, it was an exact match for DAY & MONTH & YEAR. In addition, it was not a match with ANY of the other kids in the tournament, but rather a perfect match with the kid who registered immediately before him. The odds increase!

You are right. Though, the problem might be expanded with other conditions

You should try to play in lotto :D (or maybe you should stop, as you have got one amazing result

[Garland Best]

Re: Birthday greetings

Have you mentioned somewhere math? :D Check the birthday problem http://en.wikipedia.org/wiki/Birthday_problem

The birthday problem does not apply here, it just discusses the probablility that 2 people with the same birthday exist in a group. In Aris's case we have the probability of there being an exact match with the person Aris picked, which is a much lower 1/365. Throw in the year and the odds are probably about 5 times higher, depending on the distribution of ages of kids in CMA chess events.

[Roger Patterson]

Re: Birthday greetings

not quite. there were a number of 2 people sequences - 49 if there were 50 kids in the tournament. What is being reported is something "seemingly improbable" that happened once at some time so you should also consider the total number of tournaments that Aris has ever directed where this could have happened. Plus, as it is only the seemingly improbable that gets reported, you should consider other possible sequence - e.g. the odds of two kids registering in order of their birthdays 1 day apart.

This problem of noticing something seemingly improbable and then only calculating the odds of that specific event and saying "Wow, what a coincidence" instead of caclulating the universe of all possible improbable events is quite common and is the basis of some people's belief in ESP and also some scams. See http://members.fortunecity.com/templ...an/chance.html to pick a random example off the web.

[Gary Ruben]

Re: Birthday greetings

not quite. there were a number of 2 people sequences - 49 if there were 50 kids in the tournament. What is being reported is something "seemingly improbable" that happened once at some time so you should also consider the total number of tournaments that Aris has ever directed where this could have happened. Plus, as it is only the seemingly improbable that gets reported, you should consider other possible sequence - e.g. the odds of two kids registering in order of their birthdays 1 day apart.

For a few decades I worked in a department where there were 5 of us. For a few years, 3 of us shared the same birthday, but not the same year. I don't know the odds of that.

The first year I asked the other two what they got for their birthday. One man didn't celebrate birthdays. Something to do with his religion. The other guy didn't get anything and I was sorry I asked. I did OK. I never mentioned it again in future years.

[Aris Marghetis]

Re: Birthday greetings

not quite. there were a number of 2 people sequences - 49 if there were 50 kids in the tournament. What is being reported is something "seemingly improbable" that happened once at some time so you should also consider the total number of tournaments that Aris has ever directed where this could have happened. Plus, as it is only the seemingly improbable that gets reported, you should consider other possible sequence - e.g. the odds of two kids registering in order of their birthdays 1 day apart.

This problem of noticing something seemingly improbable and then only calculating the odds of that specific event and saying "Wow, what a coincidence" instead of caclulating the universe of all possible improbable events is quite common and is the basis of some people's belief in ESP and also some scams. See http://members.fortunecity.com/templ...an/chance.html to pick a random example off the web.

Hi Roger, I believe I understand what you are saying, and I would not want to overstate the odds of what happened. However, I must admit being impressed by this incident. You see, I have run quite a few CMA events, and this was the only time that I ever had to photocopy a form, which happened to be the last registration before the late registration, and do the crossing out thing. So probably the one time this will ever happen to me, the birthdates match completely, with the ages of all the kids ranging from 5 to 14. So to a statistics layman like myself, this still seems rather cool! :)