Wednesday, July 24, 2013

My Birthday, Statistically Speaking

Today is my birthday.

Thank you for your good wishes :)

I decided that I would take a look at my database and see who in my family tree, either closely related or not, shares my birthday. My database has about 7,000 people, from all of my lines including marriage. I've done this type of search before for special days like Leap Day and the 4th of July.

In my online database I have an option to navigate based on a specific date. Entering July 24 gives me... one person. Just one!

He is George Dunckel, a very very very distant cousin through my Countryman lines in New York and Michigan. George was born 24 July 1829 somewhere in Upper Canada, and died in 1915 in Locke Township, Ingham, Michigan. He is buried in Rowley Cemetery, alongside dozens of other relations of mine. You did notice 1829, right? He is definitely older than me. Age is just a number. I digress.

But that got me thinking... how can there only be one person who shares my birthday? If my database has approximately 7,000 entries, those entries divided by 365 days in a year gives an expected number of "sharers" as 19. Birthday probability is a little trickier. Broken down in its simplest form, you only need a group of 23 people to have a slightly better than 50% chance of sharing a birthday. Do you know how many people in a group creates a near-perfect probability of sharing a birthday? 57! That is pretty mindblowing. In other words, in a random group of 57 people, the probability that two share a birthday is 99%. But only sharing with one out of 7,000 people? THAT is the statistical anomaly.

Here is a nifty calculator you can try yourself: Birthday Probability Calculator

Happy Birthday to me and George!

My mother always said I was unique. She was right.

© 2013 Sally Knudsen