Are Late-Born Athletes Overlooked? Relative Age Effects in Female Sport

Two athletes in the same age group can be almost a year apart in age. During growth, that gap can show up as differences in size and fitness — and in who gets selected. This is the relative age effect. A 2018 meta-analysis of female sport found that the relative age effect is small but real, and it grows larger at ages 14 and under and at higher competitive levels.

What the study looked at

Smith and colleagues carried out a systematic review and meta-analysis of studies on relative age effects in female sport published between 1984 and 2016.

They compared the proportion of athletes in the relatively oldest group with the relatively youngest group within each age band, and examined how the effect varied by developmental stage, competitive level and type of sport.

Key findings

• 57 studies, 308 independent samples and 25 sports were analyzed
• Across female sport, there was a small but statistically significant relative age effect when comparing the oldest and youngest groups
• The effect was larger in the pre-pubertal (11 and under) and pubertal (12–14) stages
• It was larger at higher competitive levels
• It was larger in team and individual sports with high physical demands

In other words, the bias linked to birth month is greatest where athletes are still growing, selection is intense, and physical differences decide outcomes.

How to read this in practice

• When youth athletes differ in size or fitness, consider that it may reflect developmental differences tied to birth month
• Evaluating growth over time rather than relying on a single test makes it less likely you will overlook athletes whose potential is not yet visible
• Even a small overall effect can become meaningful in selection settings at ages 11–14 or at higher levels

The included studies varied in country, sport and data collection methods. Check the original paper for the precise effect sizes (odds ratios).

Using ATHCON

ATHCON keeps a history of fitness test results for each athlete and shows the change from the previous test, so you can judge athletes not only by where they are now but by how much they are improving.

With multi-team management, you can keep records to the same standard across age groups and squads.

Takeaways

• Female sport shows a small but significant relative age effect
• It is larger at ages 14 and under, at higher levels, and in physically demanding sports
• Track development over time rather than selecting on a single test