Meta-analysis of the red advantage in combat sports.

Research has previously documented that across a range of Olympic combat sports, wearing red is associated with a higher probability of winning contests, especially when bouts are close. Yet, the hypothesis for a red advantage has not been systematically examined across multiple tournaments. Here, we report 6,589 contest outcomes for boxing, taekwondo, and wrestling from seven Summer Olympic Games (1996-2020) and nine World Boxing Championships (2005-2021). Using meta-analytic techniques, we found 50.5% wins by red for the overall data, which was not a statistically significant bias. Analyses of close contests resulted in 51.5% red wins, also not significantly different from the null expectation of equal proportions. Before 2005, however, when the red advantage was first reported and prior to changes in particular tournament rules, there was some support for a red advantage in close contests, with 56.8% of bouts won by red. It is possible that knowledge of the effect, as well as rule changes in each of the sports, have reduced the chances of a small effect being manifested, leading to the disappearance of the red advantage in competition results.