Replies

Amazing! The odds of this happening are astronomical, I bet. Any math geniuses out there who can give the odds on this?

BTW, I share a birthday with my mother, my great-aunt, and two first cousins. My second son was born 11 hours shy of sharing a birthday with us. I don't think my OB/GYN has gotten over the disappointment yet.

Regards,

Amazing! The odds of this happening are astronomical, I bet.

Don't know about that, but I do know that out of 27 randomly selected people, it is a lead pipe cinch that two of them have the same birthday (excluding the year).

First off, note that this event is no more or less likely than the four births occurring on any other specified combination of dates. So, while amazing because of the coincidence, it's really not that big a deal statistically.

Now to the numbers:

1. Assuming that impregnation is equally probable on any given month; and assuming normal variations in gestation time, one can reasonably assume that any given birthday on a given year is equally likely. (P=1/365.25)

2. Assume that impregnation is equally likely in any given year over the ~20 child-bearing years of the mother.

3. So the probability of having a birthday on any given day over that 20 years is 1/(365.25*20) = 1/7305.

4. Assuming that the births are statistically independent (perhaps not a good assumption), the probability of ANY four births occurring on specified dates is (1/7305)⁴ = ~1/3¹⁵.

Note again that any specified combination of 4 birthdays is equally likely (or unlikely).