Corrective adjustment methods for relative age effects on French young swimmers' performances

Abstract

Background: This study aimed to identify a Relative Age Effect (RAE) among French young swimmers and apply corrective adjustment procedures to rebalance performances according to categories and events.

Methods: 5,339,351 performances of French swimmers aged 10 to 18 were collected between 2000 and 2019. Birth quarters distribution was examined according to competitiveness level ('All', 'Top50%', 'Top25%' and 'Top10%'), event and age category. A linear relationship between the distribution of performances and calendar days provides a calibration coefficient allowing to rebalance performances by considering the effect of RAE for each event. Then, adjusted performances are recalculated using this coefficient, the initial performance and the relative age.

Results: Proportion of swimmers born in the first quarter was higher than the proportion of those born in the last quarter for all events and strokes (p < 0.01). RAE increases with the competitiveness level for all events. Indeed, among 'All' 12 years old 50m freestyle swimmers, the proportion born in the first quarter is 30.9% vs 19.2% in the fourth quarter, while among the "Top10%", 47.5% were born in the first quarter vs 10.3% in the last one. (p-value < 0.01). In average, each day represents a gap of 0.008 second, resulting in a difference of almost 3 seconds over a year. This tool is validated by comparing swimmers who have performed at least twice in a season. It provides a day by day rebalancing method for all swimming events and age categories.

Conclusions: Relative age effect is present among French young male and female swimmers, and is strengthened by competitiveness level. A new corrective adjustment procedure to rebalance performances considering categories and events is proposed and validated. By applying such a tool, we are able to reveal the full potential of swimmers and make it possible to compare them at the same relative age.

Fig 1. Performance means and relative age gap by age on 50m Freestyle male swimmers in 50m pools for 10-years-old to 15-years-old categories.

Fig 2. On the left-hand side, time performances pre-recalibration between 10 and 16 years old on 50m Freestyle male swimmers in 50m pool.

Horizontal bars (gold) in each age represent the threshold for the 10 Best performances (pink points). On the right-hand side, time performances post-recalibration between 10 and 16 years old on 50m Freestyle male swimmers in 50m pool. Horizontal bars in each age still represent the threshold for the 10 Best performances pre-recalibration. Three types of performances constitute the new 10 Best performances: The ones in the 10 Best pre and post-recalibration (golden points), the ones in in the 10 Best only pre-recalibration (and present on the previous graph, pink points) and the ones in the 10 Best only post-recalibration (green points). The blue points are those above the threshold (10^th performance) after recalibration and the red points below the threshold represent the blue and green points before recalibration. The rest of the points (grey points) illustrate the other recalibrated points that are below the threshold.

Fig 3. Statistical comparison of first, second and relocated performances.

*: Significant mean performance difference (p < 0.01).