What are some practical applications for the "Birthday Problem"?

Question

The "Birthday Problem" is the probability that out of some group of people, there will exist some pair of people who share the same birth day and month. It turns out that only 23 people are needed before a match is 50% probable. What can this computation be used for? What purpose does it serve other than just being interesting?

Answer 1

eggs

Answer 2

For one, it can help stop you from jumping to superstitious conclusions.  Humans tend to have superstitious minds and have a compulsion to attach deep philosophical meaning to things that seem improbable.  But if you can show there's really nothing amazing to a statistic, then you don't have to bring mysticism into the picture.

For example, my current girlfriend has the same birthday as one my girlfriends from high school.  In fact, she's from the same town too.  A mystic or an astrologer would probably get all excited over this and say "Wow, this must have some deep zodiac meaning!  What are the odds?!?"  Actually, the odds are pretty good, considering that I've dated more than 23 people in my life.  So finding 2 of them who shared the same birthday isn't all that amazing.  And since I've never moved out of state and regularly visit places in the same county, it's no surprise that most of the people I end up dating are from the same geographical area.

The birthday problem might also be helpful if you're running a school or office and want to celebrate the birthdays of students or employees.  In an office of, say, 50 employees, chances are good that some people will share the same birthday.  So instead of investing in 50 cakes, you could probably have a few joint birthday celebrations, having people who share a birthday to also share a cake.  This will cost you less money.