What does it take to be an Olympic winner? Skill? Yes. Dedication to training? Definitely. Luck? Perhaps. What colour kit you wear? Possibly.

Research conducted during the 2004 Olympic Games in Athens showed that competitors in taekwondo, boxing and wrestling who wore red clothing or body protection had a higher chance of winning. The effect wasn't large, but when the statistics were combined across all these sports it was undeniable – wearing red seemed to give a slightly better chance of winning gold. The effect has since been shown for other sports, such as football.

The researchers had a straightforward explanation for why wearing red makes a difference. Across the animal kingdom, red colouration is associated with male dominance, signalling aggression and danger to others. The vividness of the red displayed by individuals of various species has been shown to relate to the amount of the hormone testosterone they have in the bodies, which also correlates with their physical health and eventual breeding success. The researchers claimed that humans too are subject to this "red = dominance" effect, and so, for combat sports, the athlete wearing red had a psychological advantage.

In competitive sport, small advantages like this matter. The difference between winning and losing can be milliseconds, or millimetres. So, should every country be fighting for the right for their sportspeople to wear red?

Maybe they should, but not for the reasons the study authors claimed. What happened next is a textbook case of the way in which research happens, showing us why we should always be wary of neat explanations for complex phenomena.

Close calls

Like all good science, once someone has proposed a theory, others can hold it up to scrutiny. And so it was the case with the red=dominance explanation. Another research group analysed data from a different sport at the Athens Olympics, Judo, but they found that contestants who wore either white or blue had an advantage. Instead of being an effect of evolutionary colour signals, the new claim was that the difference in performance was due entirely to the visibility of the different colours. In a combat sport the person wearing the brightest clothing will be at a disadvantage – their opponent will find it slightly easier to see where they are and anticipate their next move.

Convinced? Don't make up your mind yet, because there's a further twist to the tale.

This debate was resolved in the most interesting way at around the time of the Beijing Olympics in 2008. A new study suggested that the previous theories based on dominance or visibility of the competitor were wrong. The effect wasn't anything to do with the effect of colour on the athletes, but instead to do with the effect on the referees.

I've written before about how we all have a tendency to look for causes that are somehow part of the essence of a person, and this seems to be another example. The statistics were correct, contestants wearing red really do win more, but we had been looking in the wrong place for an explanation. This study used digital manipulation to show experienced taekwondo referees fights that were identical, except for the colours worn by the contestants. Judging the same fights, referees awarded more points to contestants who had been photoshopped red than to contestants who had been photoshopped blue.

Horse play

In any competitive sport there will be close calls, situations where the margin of victory is small, and a referee has to make a judgment to the best of their abilities in the blink of an eye. It seems that because red does have an association with victory and dominance, the judgement of these marginal situations can, occasionally, be influenced by the contestant's clothes. Colour does produce a psychological effect, but it is a bias in the refs, not in the contestants.

This story provides a classic warning for anyone trying to find psychological causes for things: the effect can just as easily be in the observers as in the thing we observe. Psychology students around the world are taught the story of Clever Hans, a horse that many believed could do arithmetic. Huge crowds would pay to see Hans, held by his trainer, being asked questions such as "what is five plus two", and answer by stamping his foreleg seven times.

This seemed like a wondrous example of animal intelligence, until a psychologist showed that Hans was performing his trick by reading the body language of his trainer. Hans would start tapping his foot. When he got to the correct number his trainer would relax, and Hans would read this signal and stop. What looked like a miraculous ability to do maths, was really a clever – but not miraculous – ability to act according to what his trainer did.

So there the matter rests – for the moment at least. Wearing red could give you an advantage in competitive sports, but it’s because of the effect it has on the observers, not the observed. And, just maybe, we'll try to be a bit more careful about calling victory as we watch contests happening in the London Olympics.

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