Malcolm Gladwell has written extensively about the birthday phenomenon in sports: when youth leagues use a birthday cut-off (say January 1st), the majority of players tend to be older rather than younger. This phenomenon persists through junior hockey and seemingly into the NHL. As ESPN's Alvin Chang notes:
"People have tested this theory on several of sample groups, and it almost always holds true -- in junior leagues, the NHL and, of course, NHL draft classes."
It was nice of Alvin to link to my work on junior hockey, but unfortunately, he never read my follow-up, which noted that if we restrict our dataset just to high-scoring NHL players, the birthday bias almost completely disappears. While there might be a lot more first quarter birthdays in junior, players born late in the year are much more likely to make the jump to the NHL. It's not surprising either - if you're born in December, then you've been playing against bigger and stronger and better players for your entire life, and you have an extra year of development before you reach your peak relative to a guy who was born 11 months earlier than you. Sure, the minors are full of players born early in the year, and they are also over-represented among goons, but for the players we care about, it's not a significant effect.
Oddly,while Alvin doesn't acknowledge this effect, he draws a strange conclusion from a small number of players in the 2010 draft class:
"We tested [the 2010] class, fully expecting the usual results. But we found an anomaly. This draft class isn't dominated by North American skaters born between January and March. Instead, it's dominated by skaters born between April and June."
That's why you take more than one year worth of data, my friend! Sometimes weird things happen. Thankfully, the statisticians he consulted made no mistake:
"So, finally, we had to ask: Is this a fluke? Several statisticians told us an occasional anomaly is to be expected. Even Gladwell said, via e-mail, "One would expect wide variation from year to year. It's really long-term trends that we are interested in.""
Wow. Long-term proven trend experiences one-year anomaly.
Next time, it might be more interesting to ask general managers what they think of the late-early birthday disparity...