To test their theory, they showed 42 referees of the martial art taekwondo video excerpts from sparring rounds between similarly skilled athletes. In each video, one athlete wore blue protective gear and one wore red.
Each referee individually judged each clip, assigning points for the attacks made. They then watched the same bouts, in a different order, but this time with the colour of the protective gear digitally reversed, so that combatants wearing blue now appeared to wear red, and vice versa.
The team found that referees gave 13% more points to red competitors, even when the performances were exactly the same.
