The authors analyzed the birthdays of professional Australian Football League (AFL) players and found a disproportionate number had their birthdays in the early months of the year, while many fewer were born in the later months, especially December.
The Australian school year begins in January. "Children who are taller have an obvious advantage when playing the football code of AFL," Dr. Barnett said. "If you were born in January, you have almost 12 months' growth ahead of your classmates born late in the year, so whether you were born on December 31st or January 1st could have a huge effect on your life."
Dr. Barnett found there were 33 percent more professional AFL players than expected with birthdays in January and 25 percent fewer in December. He said the results mirrored other international studies which found a link between being born near the start of school year and the chances of becoming a professional player in the sports of ice hockey, football, volleyball and basketball.
"Research in the UK shows those born at the start of the school year also do better academically and have more confidence," said co-author Dr. Adrian Barnett. "And with physical activity being so important, it could also mean smaller children get disheartened and play less sport. If smaller children are missing out on sporting activity then this has potentially serious consequences for their health in adulthood."
Dr. Barnett said this seasonal pattern could also result in wasted talent, with potential sports stars not being identified because they were competing against children who were much more physically advanced than them. He said a possible solution was for one of the sporting codes in Australia to change the team entry date from January 1st to July 1st .
Citation: Barnett AG, Dobson AJ, Analysing Seasonal Health Data, Springer, 2010. ISBN 978-3-642-10747-4