IntelliSport

Summary

In many sports, there are more elite professional athletes born in January through May than in June through December. This phenomenon is usually attributed to annual youth age group cut-off birth dates. Conventional wisdom says that at young ages, January-born athletes are more developed than their December-born counterparts, and thus receive more coaching, putting early-year athletes on a better career trajectory than late-year athletes. However, a new study shows that late-year children aren’t weeded out, there are just fewer of them playing sports to begin with. Thus, coaches should not only be sure to divide their attention evenly to late-year and early-year athletes, but should also strongly encourage late-year athletes to sign up and stay with their sports.

Birth Date Bias Insights

Mar 12th, 2010

Experts have observed a birth date bias in several elite sports. Specifically, there are many more elite professional athletes born in January through May than in June through December. This phenomenon is usually attributed to annual youth age group cut-off birth dates. For example, if an age group cut-off date range is January 1 through December 31, there will be many January-born athletes competing against children almost a full year younger, born in December. This theoretically leads to young early-year athletes performing better than their late-year competitors due to age and size advantage, which then gets interpreted as talent by coaches. These older athletes then get access to more attentive and better coaching throughout their young careers, which increases their odds of becoming professional relative to their younger counterparts. This effect has been observed many times across many sports, including soccer, baseball, ice hockey, and tennis.

However, studies showing this birth date bias may have been flawed. Scientists have long assumed that there are the same number of late-year children signing up for youth sports as early-year children. Thus, the theory goes, more late-year athletes get weeded out of the sport due to their age disadvantage, leaving more early-year athletes to make the pros. However, a recent study* of French soccer players has shown that there are significantly fewer late-year children signing up for and playing youth sports than early-year children. This suggests that the late-year children aren’t weeded out, there are just fewer of them playing sports to begin with. Thus, conventional thinking about the birth date bias may be wrong.

The results of this study suggest that less coaching attention may not be the reason why fewer late-year athletes end up in the professional ranks. Instead, we should try to understand why there are fewer late-year children than early-year children who want to participate in youth sports. The authors of the study believe that late-year children could be discouraged from signing up because they are smaller than their early-year counterparts, or that late-year children have higher drop-out rates than early-year children. Thus, coaches should encourage these late-year athletes to stick with the sport, because the size and age advantage diminishes with time. While the conventional theory may play a role in determining why late-year players fail to make the pro ranks as often, we should be aware of the other factors suggested by this study. Coaches should not only be sure to divide their attention evenly between late-year and early-year athletes, but should also strongly encourage late-year athletes to sign up and stay with their sports. This way, sports can retain future elite athletes who would otherwise be lost simply because of their birth date.

*Delorme, Nicolas, Boiché, Julie and Raspaud, Michel (2010) 'Relative age effect in elite sports: Methodological bias or real discrimination?', European Journal of Sport Science, 10: 2, 91 — 96

By IntelliSport

Implementation

• Divide attention evenly between late-year and early-year athletes, to prevent talented late-year athletes to falling short of their potential.
• Encourage late-year athletes to sign up and stay with their sports, since size and other age-related differences disappear over time. Late-year athletes shouldn’t get discouraged by these factors.