The Relative Age Effect of Participants in the World Junior Tennis Finals in 2012–2016

The main aim was to verify the Relative Age Effect (RAE) between female junior tennis players (U14, n=240), participants of the World Junior Tennis Finals in 2012–2016. The secondary aim was to verify the RAE on the order of nomination to each national team and then verify the RAE on the final ranking of the teams. The third aim was to compare the RAE between junior female tennis players and the world's best senior female players. Chi-square test and Effect Size (ES) index w were used for statistical data analysis. Statistically significant RAE was found in each of the years 2012–2016 for all subgroups, ES ranged between medium and large. Statistically significant RAE was found for all female players over the entire five-year period, ES was medium. Statistically significant RAE was found in all cases for nominations of players (the first, second and third tennis player of team), ES ranged between medium and large. In all four performance groups (1st-4th, 5th-8th, 9th-12th, 13th-16th), the RAE was statistically significant, ES was medium and large. Comparison of RAE between the groups of junior tennis players and the world's best players showed non-significant differences, the ES was small. Keywords: Date of birth. Chronological age. Age distribution. Youth sports. Sports.