Outliers: The Story of Success · chapter 1 · id outliers-c1-01-canadian-junior-hockey-players
“Canadian junior hockey players are disproportionately born in January-March because the January 1 age cutoff gives older children a physical maturity advantage, leading to better coaching and more ice time -- a self-reinforcing cycle.”
TRUE, BUTconfidence: medium⚠ extracted by pipeline, re-audit pending
Receipts
Barnsley & Thompson (1988), Canadian Journal of Behavioural Science 20(2)DOI registry: valid
Approximately 40% of OHL players were born in January-March versus roughly 10% in October-December, against an expected ~25% per quarter.
Cobley, Baker, Wattie & McKenna (2009), Journal of Sports Sciences -- meta-analysis of 130 studiesFLAGGED: DOI not in registry
The relative age effect is well-documented across multiple sports. Ice hockey showed the largest effect sizes of any sport studied.
Gibbs, Jarvis & Dufur (2012), International Review for the Sociology of Sport 47(5)FLAGGED: DOI not in registry
Among players who make it to the NHL, those born in Q4 (Oct-Dec) tend to have longer careers and score more points per game than Q1 players -- the 'underdog effect.'
Fumarco, Gibbs, Jarvis & Rossi (2017), PLoS ONEDOI registry: valid
Among NHL All-Stars and top performers, relatively younger players (Q3-Q4) were overrepresented. The selection pipeline filters out average Q1 players who were selected for size, not skill.
This claim is a stable, citable object. If you can falsify a verdict, tell us. Corrections are loud here.