Malcom Gladwell's "Outliers" book shows some interesting relationships between month of birth and professional sports players. Basically those born earlier in

Malcom Gladwell's "Outliers" book shows some interesting relationships between month of birth and professional sports players. Basically those born earlier in the year will generally have a physical advantage, which at a young age can make quite a difference (think of a chiold at 6 yeard old exactly compared to a child whi is 6 years and 11 months old). These kids are then singled out and given extra training for the sport which they are good at, which compounds the effects. https://en.wikipedia.org/wiki/Relative_age_effect https://en.wikipedia.org/wiki/Relative_age_effect