The relative age effect in Australian Football League players

Youth sports teams are usually grouped into yearly age groups based on fixed cut-off date (September 1st in the UK and January 1st in Australia). Children born just after this cut-off will be the oldest and most mature in their age group. This gives them an advantage in competitive sport, an advantage which has persisted into adulthood as shown by seasonal patterns in the dates of birth of professional ice hockey, football and basketball players. We were interested in whether a similar seasonal pattern exists in professional Australian Football League (AFL) players. We examined all AFL players in the 2009 season excluding foreign-born players. We compared the observed number of players’ born in each month with the expected number based on national statistics. There was a marked and statistically significant seasonality in players’ dates of birth. There were 33% more players than expected with dates of birth in January, and 25% fewer in December. Players who are relatively older in youth AFL teams have a better chance of turning professional.