Color of judo uniform has no effect on winning

In judo competitions, athletes wear a blue or white costume called a judogi. Traditionally, the first called player always wore blue, but after a rule change in 2011 the first called player switched to the white judogi. Before this it was commonly thought that those honoured with the blue outfit are more likely to win the competition, with little attention paid to the skill of the athlete.

Contrary to previous studies and widespread belief, a significant win bias for the first called athlete was found, regardless of the colour of judogi they wear. Dr Peter Dijkstra from the Central Michigan University conducted the study along with his colleagues Dr Paul Preenen of The Netherlands Organisation for Applied Scientific Research and Hans van Essen from Judoinside.com.

For this study, the researchers developed the most extensive judo contest dataset to date using sources like the Olympic Championships and Judo World Cups. This, combined with an exceptional rule change, enabled them to isolate the effect of uniform colour on winning.

"A unique policy change in judo switched the uniform colour assignment of the first called athlete, who is normally known to be the better athlete," Dr Dijkstra explains. "The change showed that before 2011 the blue judogi athletes won more matches, and, not surprisingly, after the colour switch the white judogi athletes won more contests. We found that there was no effect at all of uniform colour itself on winning in judo."

So, given these results, why do so many believe that the colour of the outfit an athlete wears has any link to their chance of winning?

This could be due to psychological effects that some uniform colours can have on winner bias. "There is very strong evidence that red colouration increases winning because this colour has an intimidating effect on opponents," says Dr Dijkstra.

The researchers believe their findings may be relevant for other sports where policy makers are concerned about color biases in winning.

"We have shown that using a blue-white pairing ensures an equal level of play in judo. This colour pairing could be an alternative for sports where red-blue pairings are commonly used," suggests Dr Dijkstra. "Given the strong association that sports fans have with their team's colour a change is not going to happen overnight. But it should be considered in competitive sports, if we want to level the playing field."