James Robert Deaner, of Grand Valley State University, was setting out to find if there was a link between a hockey player's facial shape and aggression and where he was drafted in the National Hockey League draft, when he discovered something else: There's an apparent link between the month in which they were born and their selection position in the draft.
According to Wired.com:
They found that, on average, NHL draftees born between July and December comprised 34 percent of those drafted, but played in 42 percent of the games and scored 44 percent of the points. On the other hand, those born in the first three months of the same year comprised 36 percent of drafted players but played in just 28 percent of games and scored 25 percent of the points.
The researchers focused on Canadian players because Canadian youth leagues assign players by age, with a December 31 cut-off date. That makes it easier to compare players who are the same age but were born at different times of the year.
If you're a parent, you probably know this scenario because it's hotly debated in education. Is the younger child able to keep up with the older children when they start school, or is it best to wait a year?
Freakonomics considered this question more than a year ago in its piece, "The Disadvantage of Summer Babies."
It reported on a study of European soccer players:
Forty-three percent of players were born in the first three months of the year, while only 9 percent were born in the final three months. Children who are a few months older than their peers at 5 or 6 have more developed cognitive and motor skills, which makes them more advanced athletes and students. This early advantage can lead to self-fulfilling prophecies later on: the child thinks she is an underachiever, and so will often play that role.
Or maybe it's all just random luck. It's a tough gamble for parents who aren't as interested in whether their kid becomes a professional hockey or soccer player, but just want to know whether to wait to start a younger kid in school.
For this, we defer to J.L. Cook and G. Cook, authors of Child Development Principles and Perspectives:
The research evidence does not argue strongly for older entry ages. Some studies indicate a small advantage for some skills for older children, but the difference fades within the first few years of schooling. For most skills studied, schooling has a significantly stronger effect than age, and younger children at a grade level benefit from schooling as much as older children (Oshima & Domaleski, 2006; Stipek, 2002). There also may be some risks for children who are older than their classmates because of delayed entry. These children show more behavior problems than younger children at the same grade level, with some studies finding that the difference increases over time while others show no long-term disadvantages (Byrd, Weitzman, & Auinger, 1997; Lincove & Painter, 2006; Mayer & Knutson, 1999).
In other words: On this question, a parent has to resort to gut instinct. Kind of like people drafting hockey players do.
There is also a birthdate correlation to major league baseball players. July 1 is the cutoff date for many Little League and other developmental leagues.
Malcolm Gladwell tackles this issues in Outliers as well.
This is the lead author of the new study, Robert (not James) Deaner.
Wired made a mistake and corrected it. I hope it can be corrected here.