danlo wrote:
mjs82 wrote:
So far we have:
January 5th 1985
January 9th, 1990
27th of January, 1984
31. januar 1988
February 7th, 2001
February 11,
04/09/1990
April 24,1990
may 20 1983
May 21st, 2003
May 26th, 1964.
June 12, 1988
June 23 1983
August 22, 1972
October 19th, 1966
1st November 1964
November 2nd, 1973
november 27, 1961
28th december, 1961
and mine's December 13th
Statistically, in a group of 23 people, the odds approach greater than 50-50 that at least two of them share the same birthdate. We need two more to see what happens. In a group of 41, it approaches 90% then levels off.
How can the odds approach greater than 50-50 that two will share the same birthdate, when there's only 23 dates in the pool? There's still 342 different dates it could be.
It's all to do with probabilities. At first glance the odds would appear to be as some have suggest, 1 in 365.25. But, this does not take into account the principal of stacked arrays:
For a 23 group sample:
(1) Probability of at least one coincident birthday
This is 1 - Pr(no coincident birthday), where the lack of a coincident birthday leads to an occupancy diagram of
[1,..,1] [0,...,0]
(23) (342)
U is then 365!/(23!342!), while B is 23!/(1!)23 (0!)342 = 23! and thus Pr(no coincident birthday) = 365-23 x 365!/342! = 0.493, so that Pr(>1 coincident birthday) = 0.507, from which the original Birthday Paradox follows.
Sorry for my late reply, I only just stumbled over this thread again for the first time in weeks.