Adam Brucker Online

Interesting stuff on Wikipedia about “The Birthday Paradox.”

http://en.wikipedia.org/wiki/Birthday_paradox

In particular, many children are born in the summer, especially the months of August and September (for the northern hemisphere) [1], and in the U.S. it has been noted that many children are conceived around the holidays of Christmas and New Year’s Day; and, in environments like classrooms where many people share a birth year, it becomes relevant that due to the way hospitals work, where C-sections and induced labor are not generally scheduled on the weekend, more children are born on Mondays and Tuesdays than on weekends. Both of these factors tend to increase the chance of identical birth dates, since a denser subset has more possible pairs (in the extreme case when everyone was born on three days, there would obviously be many identical birthdays). The birthday problem for such non-constant birthday probabilities was tackled by Murray Klamkin in 1967. A formal proof that the probability of two matching birthdays is least for a uniform distribution of birthdays was given by D. Bloom (1973)