Today is February 29th. Given that it comes only once every four years, that would make it a rare birthday. But it is even rarer. As Andrew Leigh and I discovered in a paper just published in the Economic Record, the birthrate on this day is about 10% lower than if it was an ordinary Wednesday. Why? Parents like to move their children’s birthdays off days like this and on to something more regular. Of course, if today was a Friday they might get some resistance from their doctors who don’t want those births pushed on to the weekend.