I looked at the birth month of the 290 players on the rosters of the Men's U23 teams that played in the 2012 London Olympics. This shows that deficit of quarter 4 birth months again.
The actual numbers show the deficit a bit clearer. There are almost half as many Q4 birth months as Q1 birth months.
Q1 Q2 Q3 Q4
84 79 82 45
Now let's look at birth month for all the players 1989 to 1993 lined up sequentially. We can compare the number of Q4 (red bars) to Q1 (blue bars) players who are almost the same age. So we can compare Q4 1989 to Q1 1990, and see if Q1 players, who are slightly younger but born in Q1, are more numerous than the similarly aged Q4 players.
First we see that older players are more common and the frequency drops off steadily by year. But look at the red and blue bars. In all of the 4 years, the red bars are lower than the adjacent blue bars---despite the red bar players being a little older than the adjacent blue bar players.
Note, there is some fluctuation in birth month frequencies. In the US over the last 10 years, ca. 24% of all births have been in Q1, 25% Q2, 26% Q3, and 25% Q1. I don't know the frequencies in the 16 countries involved here, but the US data would not make me think that Q1 births are more common than Q4. Certainly the magnitude of differences seen in the Olympic rosters is much larger than what is seen in natural birth quarter differences.
Next post looks at the deficit of December birth months on Division 1 NCAA (US) male soccer teams. That is a follow up on an examination of Q4 birth month deficits on the US Soccer Development Academy (USSDA) teams.
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Related work:
Williams (2009) Relative age effect in youth soccer: analysis of the FIFA U17 World Cup competition
http://onlinelibrary.wiley.com/doi/10.1111/j.1600-0838.2009.00961.x/full
The actual numbers show the deficit a bit clearer. There are almost half as many Q4 birth months as Q1 birth months.
Q1 Q2 Q3 Q4
84 79 82 45
Now let's look at birth month for all the players 1989 to 1993 lined up sequentially. We can compare the number of Q4 (red bars) to Q1 (blue bars) players who are almost the same age. So we can compare Q4 1989 to Q1 1990, and see if Q1 players, who are slightly younger but born in Q1, are more numerous than the similarly aged Q4 players.
First we see that older players are more common and the frequency drops off steadily by year. But look at the red and blue bars. In all of the 4 years, the red bars are lower than the adjacent blue bars---despite the red bar players being a little older than the adjacent blue bar players.
Next post looks at the deficit of December birth months on Division 1 NCAA (US) male soccer teams. That is a follow up on an examination of Q4 birth month deficits on the US Soccer Development Academy (USSDA) teams.
------------------------------------------------
Related work:
Williams (2009) Relative age effect in youth soccer: analysis of the FIFA U17 World Cup competition
http://onlinelibrary.wiley.com/doi/10.1111/j.1600-0838.2009.00961.x/full
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