Phoenix Coyotes goalie Smith plays the puck with Los Angeles Kings' Kopitar during the second period of Game 4 of the NHL Western Conference final hockey playoffs in Los Angeles
If you are Canadian and your birthday falls earlier in the year, you're more likely to be drafted by the NHL than someone whose birthday comes later. But that doesn't necessarily mean you're a better player. Reuters

If you’re an aspiring National Hockey League star born in Canada in July through December, you may have had a hidden handicap your whole life. A new study shows that the NHL draft may have been overestimating the talents of players who are relatively older within their year of birth.

Grand Valley State University psychologist Robert Deaner and his colleagues were interested in examining relative age effects, which is where people relatively old for their educational or academic age groups are more likely to succeed. The phenomenon is well-documented in hockey, where the oldest boys in age groups are more likely to make elite teams and receive attention.

Yet it is still unclear how much of this pattern is due to natural development – an older boy is generally bigger and stronger than a younger one, after all, and a coach wants to build the strongest team possible -- and how much is due to selection bias irrespective of a boy’s ability.

“Success correlates with relative age, but we don’t know how you get that pattern,” Deaner said in a phone interview.

Deaner and his team decided to take a look at Canadian players who made the cut in NHL drafts from 1980 through 2006. (In Canada, youth ice hockey age groups are standardized with a Jan. 1 birthday cutoff date, making it easier to study age-related effects.)

The researchers compared a draftee’s birth date and draft position to his professional productivity, as measured by games played and points scored. Their results were published on Wednesday in the journal PLoS ONE.

According their data, it still pays to be born in the first quarter of the year. Thirty-six percent of NHL draftees were born between January and the end of March, while just 14.5 percent were born in the last quarter of the year. But players born in the last half of the year are more likely to have successful careers – playing 42 percent of the games and scoring 44 percent of the points accumulated by the players in the study, despite being underrepresented.

“Relatively younger players are excelling more than you’d expect based on when they’re drafted,” Deaner explained.

Though the preference for older players has held nearly constant for 27 years, the career data from Deaner and his colleagues shows that this relative age bias can be irrational.

But what makes a younger player turn out to be more successful in the end? There’s a theory about an "underdog effect," where younger boys are strengthened by having to compete against older and stronger peers, but nothing has been proven yet.

“It’s possible younger players have always had to work harder and be more persistent,” Deaner says. “Then, maybe, when they’re struggling in the minor leagues they may be more likely to work on their skills than go out for beers.”

There’s also the fact that the NHL looks at certain elite hockey leagues in Canada when evaluating potential draftees. Boys at the older end of their age group are more likely to make it into these groups when they’re 13 or 14, which could put them on an easier path to success in their late teens and earlier twenties. In those intervening years, there could be room for the younger players in the age group to improve their skills.

Though NHL scouts and team officials are aware of age-related effects, the results show that they still drag down the drafting process a bit.

“Even among professionals that get paid to evaluate talent, something related to birthdays is leading them astray,” Deaner said. “It’s surprising that professional decision makers can be biased in that way.”

So, younger hockey players should not necessarily lose heart if they are in an age group with much older teammates. They might not be getting picked for the top slot on the team right away, but they could end up more successful in the end.

Age-related effects have both positive and negative consequences outside the hockey rink as well. Italian researchers discovered that relatively younger students within their university cohort tend to study more and perform better academically, though they were less likely to have an active social life (though maybe that’s correlated with all those extra hours in the library).

More soberingly, a child that’s born a month before his or her state’s cutoff date for kindergarten, thus making them one of the youngest children in their class, is much more likely to be diagnosed with attention deficit hyperactivity disorder, and to be on medication for ADHD later on.

SOURCE: Deaner et al. “Born at the Wrong Time: Selection Bias in the NHL Draft.” PLoS ONE published 27 February 2013.