Malcolm Gladwell capitalized on research conducted by Roger Barnsley (et al., 1985) by suggesting in his 2008 book, Outliers, that there is an “Iron Law of Canadian Hockey.” This theory is also known as the relative age effect in psychological research and it suggests that the older a player is when they begin training for a sport, the more likely they are to achieve success in that sport.

In fact, in a talk posted on YouTube, Gladwell goes even further, saying, “In absolutely every system in which hockey is played, a hugely disproportionate number of hockey players are born in the first half of the year.” He says this in the context of a talk about society not taking advantage of opportunities to improve human potential.

“Logic tells us there should be as many great hockey players born in the second half of the year,” suggests Gladwell, “as born in the first half. But what we can see here, there’s almost no one born it the end of the year, everyone’s from the beginning.”

But is this actually true — are more elite hockey players born in the first half versus the second half of the year?

I was listening to this talk and couldn’t help but wonder, “This seems like a really perhaps-too-neat result. Is this actually true? Does the relative age effect impact your likelihood to be a great hockey player?”

So first I went over to Wikipedia and found this list, List of 100 greatest hockey players by The Hockey News from 1998. This is a quick and dirty way of testing the hypothesis at face value — are the hockey greats of the world more likely to have been born in the first half of the year?

Only 39 of the hockey players on the list have Wikipedia entries, so they were the easiest to verify their date of birth. Of those 39 players, 20 were born in the first half of the year, and 19 were born in the second half. Hmmm… that doesn’t really seem to jive with Gladwell’s claims. ((Yes, I realize this isn’t robust research — it’s an arbitrary list and only 39 out of 100 datapoints were examined, but there’s no reason to suspect that those 39 datapoints were not fairly random.))

So finding some support that perhaps the issue isn’t as clear-cut and dried as Gladwell suggests, I turned to PsycINFO, the psychological research database. It didn’t take long to find a study that had the same questions I did — does the relative age effect (RAE) actually predict excellence in sports?

Gibbs, Jarvis & Dufur (2012) suggest that the answer is no. In a far more systematic approach than my quick and dirty review of a top 100 list, the researchers examined the distribution of birth months for the first round draft picks of Canadian players in the NHL for the years 2007-2010. Then they looked at 1,109 players who played on major league rosters from 2000-2009.

Last, they examined All-Star and Olympic hockey rosters from 2002-2010. These are the elite players of hockey — the cream of the crop.

So what did they find?

In our analyses, we found a strong relative age effect that eventually fades, then reverses across levels of hockey play among Canadian-born players.

In our first data, early birth-month advantage is apparent in the Medicine Hat Tigers championship roster of 2007 (56%) and for their opponents the Vancouver Giants (44%), but it is less true of the same teams three years later (33% and 39% respectively). [These were the teams Gladwell highlighted in his book chapter.]

The effect is also apparent among Canadian-born first round draft picks, with 40 percent, 41 percent, 47 percent, and 33 percent born in the first quarters of 2007, 2008, 2009, and 2010 respectively.

But for the average player in the NHL, the effect seems to fade. Although the first round draft picks confirm Gladwell’s law (33–47 percent across 2007–2010) — a reflection of their Major Junior Hockey performance — the percent of all Canadian hockey players in the NHL born in the first three months is a modest 28 percent.

But it gets worse. Among the most elite hockey players, the effect completely reverses — it’s better to be born later in the year if you want to become one of the great hockey players: “The combined average of the All-stars and Olympic rosters [born in the first three months of the year] is 17 percent.” Compare this to the 28 percent noted above and you see that it actually hurts your chances to be born earlier in the year if you want to play in the Olympics or on an All-Star team.

Last, the researchers found one more perhaps-not-so-surprising result — players born earlier in the year have shorter hockey careers — an average of a year less than those born in the last three months of the year (Gibbs, Jarvis & Dufur, 2012).

The incongruous findings come from Gladwell confusing simply playing on a team with being an elite player in that sport. He defined success in hockey as simply making the team — a way most people who play sports probably wouldn’t agree with. The researchers sum it up nicely:

Our findings illustrate how critical it is to define hockey success. When hockey success is defined as playing Major Junior Hockey, the effect is strong, as Gladwell reported in the popular press.

But the effect diminishes when success is defined as making the NHL, and fades when performance and skill are considered.

When hockey success is defined as the most elite levels of play, the relative age effect reverses.

Who Will Tell YouTubers?

Now here’s the real problem — these YouTube talks and videos don’t get updated or removed. Nobody is going to come along and point out that the things Gladwell says in this talk aren’t necessarily true based upon our latest understanding of the research. ((Gladwell’s talk was apparently conducted in 2008, prior to the new research being published.))

Remember his line, “Logic tells us there should be as many great hockey players born in the second half of the year.” Well, actually the data suggests that this is, in fact, true after all.

And that’s the challenge of disseminating pop-psychology tidbits on video and in books — their conclusions will remain forever etched ((Unless someone goes back and edits these things, which is rarely done.)), while the science and research data continue to march forward.

Finally, it’s a reminder that psychology and sociology data rarely results in neat, clean conclusions. While initial research might draw such conclusions, later more-nuanced, rigorous research often demonstrates the problems with those first studies.

Watch the Gladwell YouTube talk: Malcolm Gladwell Explains Why Human Potential Is Being Squandered

Read Ben Gibbs’ blog entry on his research: Relative Age Effect Reversal Found At Elite Level of Canadian Hockey