I think it makes sense that an early month birthday skews the results. From the first time kids play in age brackets, the kids with early birthdays have an extra half year of development on the late birthday kids. When you look at the difference a full year makes, ie comparing 15 yr olds to 14 yr olds, you can see which age group is going ot get more focussed coaching, more ice time, and more encouragement to continue at a high level.

A more interesting (and involved study) would look at whether the so-called late-bloomer players tended to be late birthday kids - underdeveloped at younger ages.

So, the fact that I'm born in December provides a sufficient excuse as to why I suck at hockey? Cause I could really use an excuse.

Yeah, I misspoke. There's a very logical reason for the phenomenon to exist, but no reason to be content with it.

I can't find the stats I'm looking for to prove this, but aren't more babies born in the first six months of the year than the last six? There was always a torrent of birthdays in the spring, when I was in elementary school.
75% seems high, but I'd be willing to believe 60% of Canadian kids are born January to June -- something that would negate the "bias" you've found in the NHL, anyway, and weaken the Toronto Star findings a bit.

This crazy study I stumbled across shows a pre-July bias for NHL players, but the author believes it has something to do with astrology...

I'm full of shit. In 1995, 50.7% of all newborn Canadian babies born were born Jan-June. Nowhere near 60%...

check out Levitt and Dubner (Freakonomics) for some research on birth date and sports success as well as Steve Sailer on his blog for some rational explanations
Pedro

There is a bias towards "bigger, stronger players", what is wrong with that? If bigger and stronger makes the player seem better to the coach of the team, is it not in our best interest to have the best players on the ice?

Or am I misunderstanding the point of this post?

I think the point is that early birthday kids have an inherent advantage in that they are "bigger and stronger" within their peer group because of the way the peer group is generally defined - by calendar year. Unless you think that early birthdays lead to bigger and stronger full-grown adults.

It would be interesting to see not just early vs late birthdays, but also by month. For most high school students, birthdays after Sept 1st are eligible to play at the next lower level, making them the oldest. I always found this as odd, as it is another arbitrary date that they for some reason was thought to be more fair. I wonder if this has had an affect on those hockey players...

I can't find the stats I'm looking for to prove this, but aren't more babies born in the first six months of the year than the last six?

I just looked at BC (any Ontarians are welcome to report back from the Ontario Department of Vital Statistics...) and the only years where births by month were available were 2004 and 2003. Of roughly 40,000 live births in each year, 50.2% were in the first six months of 2003, and 49.6% in the first six months of 2004. If the Null Hypothesis is that birth rate is constant over the year, I think we need some other data points to falsify it, certainly to the extent of explaining a roughly 60/40 advantage in professional hockey...

A lot of work has been done on how age impacts kids in school. The work of Jean Piaget in cognitive development suggests that the development of the brain has a profound impact on children’s ability to learn. A child might be having difficulty because they may not be developmentally ready to learn a particular concept. They will learn the concept, but only when their brain has developed enough to do so.

This has serious implications in school since an elementary student might be achieving poor results not because he/she won't learn, but simply because she/he can't learn at that particular moment because his/her brain isn't developed to learn the concept. There is much more to brain development than age (i.e. environment, nutrition, sleep, activity, exploration, and exposure to new ideas), but cognitive development is a vital part of learning.

Imagine the youngest student in the class being, physically, the smallest in size, but also the one whose brain is the youngest and perhaps the least able, developmentally, to grasp new concepts. What is the emotional impact of being physically behind everyone else in the class?

Think back to when you were in elementary school. The strongest students and the biggest kids in the class were, more likely than not, the oldest. While this will even out in the long run, the psychological and emotional impact that this has upon kids can impact them for life. Studies have been done about the impact that the Relative Age Effect has upon children's self-esteem, overall success in school, and even likelihood for suicide.

We should not be content with the effect that month of birth—or, I think more precisely, brain and physical development – has upon children. Its impact is receiving a great deal of research, and, if it's any consolation, teacher's colleges are rife with discussion about cognitive development and the work of Piaget. A part of me, however, wonders if this is the kind of information that people cram, regurgitate on test day, and then forget. Certainly, parents and coaches should be aware of cognitive development and the way that it impacts children’s lives.

A few years basck I read a study that dealt with this issue in detail and the results show a series of advantages that add up to aid early in the year kids. Firehead pretty much hit the study's results on the head: the kids with the earlier birthdays typically have a commensurate increase in size and coordination. This gets them on the higher calibre leagues where they receive better coaching and better facilities. The smaller kids on the other hand end up in the lower levels with less experienced coaches (i.e the rich get richer, the poor get poorer). Sure there will always be exceptions, but children's growth curves are pretty predictable and older pretty much always means bigger and more coordinated.