A reader named E. Allyn Smith, a Ph.D. student in linguistics at Ohio State University, wrote in with the following observations.
I’ve been thinking about birthdays a lot lately, because November 15th to the 27th is one of the annual “birthday rushes” in which I have eight birthdays in two weeks. It got me thinking that not only are there a lot of birthdays in that short period of time, but two of the days in that interim have more than one birthday. It reminded me of the birthday problem in mathematics (see more about this here) in which, once you have 23 people in a room, there’s a larger than 50 percent probability that two of them will have the same birthday.
In a similar vein, I became curious about a variety of properties of the birthdays I keep track of in my calendar. Here are some facts that I found (if I don’t have your birthday, feel free to leave it in the comments section “in the name of science”):
Total number of birthdays on my calendar: 51
Number of weeks in a year: 52
Of those weeks in a year, here’s the breakdown of how many birthdays I have in a given week (obviously this changes year to year, but not significantly):
0 people – 22 weeks
1 person – 15 weeks
2 people – 11 weeks
3 people – 2 weeks
4 people – 2 weeks
Number of days with more than one birthday: 5
Greatest number of birthdays in a two-week period: 8
Greatest number of consecutive weeks with no birthdays: 6
Upon discovering that so many weeks had no birthdays (in addition to the six-week stretch, there were also periods of four and three weeks at a time with no birthdays), I thought back to the horoscopes in magazines like Seventeen, in which they list your personality on the basis of your zodiac sign, as well as the compatibility (or lack thereof) between different signs. So I decided to see whether the birthday-dense times in my calendar correlated with my “compatible” zodiac signs, while the birthday-sparse periods correlated with my “non-compatible” zodiac signs.
The first thing I noticed was that my two “rush times” don’t fall into individual “signs” (for example, Nov. 15 to 27 spans both Scorpio and Sagittarius), but the next thing I noticed is that I’m supposedly not compatible with either of those signs. Let me point out that this group includes my college roommate (and we all know that you’d have to be pretty compatible to choose to live with someone in a dormitory room for a second consecutive year) as well as my brother. Meanwhile, the six-week no-birthday period extends from the last three weeks of Pisces through the first three weeks of Aries. Even in the weeks on either side, I only have one birthday, but I supposedly am compatible with Aries and Pisces.
Conclusion: either 1) zodiac “compatibility” is bunk (my personal favorite); or 2) I’ve managed to make friends primarily with those I’m not compatible with while simultaneously avoiding people with which I would be compatible. I reserve the right to do further research on this topic.