Originally posted by

**Iconoclast**View PostAnd same for you. And probably many others here on the boards.

As I say, a lot of things about probabilities are not intuitive and show common sense is wrong.

(you work out the odds of gathering 30 people and for them not to have a birthday in common; to simplify that divide the probability equally over the year, but that's not true I don't think, so to get the real probability requires a lot of birth information, and that takes all the fun out if it). Oh, if you want the year to be the same, then gather all the kids in a common grade at a school. You'll have a few that share birthdays and they probably even know each other.

The also having a child with same birthday is cool though, and that is probably much less common. So that's so improbable I'll hypothesize that you two must have planned it that way. I mean really, of all the days in your adult life that your child could have been born, and hers could have been born, it just happened to be the same day? Let's see, about what, 35 years for fertility (your female friend) so the combination has a 1 in 163.4 million chance (making the floorboards and phonecall absolutely run of the mill common). So clearly the two of you discussed that and made it happen. Just keep this in mind when you start to think about relating post hoc probabilities for known events to evaluating hypotheses that only occur to us after we know the events happened.

- Jeff

## Leave a comment: