I would like to know what the odds are of having two siblings in the same family with the same birth date. It happened to two of my children and I found that to be quite remarkable. Perhaps it isn't as remarkable as I think and I am interested in knowing any statistics on something like this.

-- jane nelsen (pjkknelson@aol.com), December 31, 2001

Answers

The odds would be less than 364 to 1 (i.e. a greater than 1/365 chance of the second born with the same birthday as the firstborn). With more than 2 children, the probability increases since there is more than 1 pairwise relationship.

-- Jon Miles (jon@milesresearch.com), January 02, 2002.