Tricia Meyer

Affiliate Marketer, Blogger, and Consultant

Social Media Friends and the Birthday Paradox

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I was noticing last night that of my 400 Facebook friends, 5 of them have a birthday on Thursday. That’s not including the ones that are businesses with a “start date” of the end of the year or friends who do not allow access to their birthday. I mentioned to my husband that it was improbable. With 365 days in a year, I should only have one birthday friend per day–two tops. He started talking about the “birthday paradox” and how if you put only 23 people in a room, you would have 2 people with the same birthday. I thought he was nuts. I mean, 365 days? Out of 23 people 2 will have the same birthday?

So of course I did a search for it. I found the “Birthday Problem” Wikipedia page, which explains that if you have 23 people together, there is a 50% chance that 2 of them will have the same birthday. If you get 57 people, there is a 99% chance that 2 of them will have the same birthday. It still doesn’t seem possible. 366 possible birthdays. 57 people and you have a 99% chance of the same birthday popping up?

Here is where YOU come in. I need a little help from my social media friends because I can’t get 23 or 57 people into a room today. Can you leave a comment below with your name and your birthday? I don’t need the year. Leave your name so I can verify you’re real people when two birthdays pop up the same and it isn’t just someone messing with me. I’ll make a little chart and we’ll see how many people have to comment before we get the same birthday. Curiosity has gotten the best of me now!!

Edited: It took only 18 people posting to get our first repeat birthday. We defied the odds! And my husband proved, once again, that he is better at math than I am.

Comments

  1. Mine is Jan. 18th and I saw that was your 5th comment! I guess your experiment was done a long time ago. I’m researching the birthday paradox, so that I can do it w/ my 5th graders as an introduction to our probability unit. I love that you used the computer to get your info. We’re going to display ours at our science, math & technology fair. So I’ll be sure to mention this site. Thanks!

  12. November 8th.

    Interesting…I just checked my FB. I have 3 days during the year that I have 4 friends with the same birthday…including Cindy’s birthday! My DH and a good friend have the same birthday…year and all.

  15. Sept 14 for me.

    Can’t wait to see how this turns out! Interestingly enough, we have a high occurence of this in my extended family. Sept 15 is a big day for us–one nephew, one SIL, another SIL and an aunt all the same day! Also Dec 3–my sis, nephew and BIL! And my college roommate had the same birthday as me–we were actually born about an hour apart. It’s crazy!

  16. April 18

    I’ve read this stat before and it’s true! I’m interested to see what you come up with-

  21. September 7th

    Interrsting tidbit for you — my husband and daughter have the same birthday – January 27th.

  23. Interesting. Mine is Sept 10th. I will say that growing up there was a guy in my class that shared my birthday so there is probably some truth to that.