Several times now I’ve been in a classroom situation where the professor has mentioned the well-known birthday paradox, and had the time and people to perform a demonstrative experiment, but didn’t seem as interested as I was. This morning I realized I could perform the experiment on my own without having to bother anybody else thanks to the magic of Facebook profiles. Since most people have their birthdays listed, I just opened up my list of friends alphabetically and starting listing birthdays to see how long it would take before one of them repeated:
Statistics says that there isn’t a better-than-average chance of a birthday collision until a group has at least 23 people in it. For only 13 people, as we have here, the probability of a collision is only
1 – (365!/352!)/36513 = 19.4%
Everybody try this at home!