Are referees biased in favor of red uniforms?

A month or so ago, I posted about a study that -- very surprisingly -- found that teams wearing black uniforms tended to be more aggressive, picking up extra penalties. In the comments, an anonymous poster referred me to two additional studies, with even more shocking results.

First, there's a May, 2005 study in "Nature," by Russell A. Hill and Robert A. Barton. (The study isn't online, there's a story about it.)

The authors examined matches in combat sports from the 2004 Olympics. In those contests, one competitor always wears blue protective gear, and the other wears red. Which wears which is chosen randomly.

Hill and Barton found that the guy in red beat the guy in blue a statistically significant portion of the time -- about 55%, roughly the size of the home field advantage in baseball. When the opponents were of roughly similar ability (the study doesn't say how they measured this), the fighter in red won about 62% of the matches. That was significant at 1.4%.

Now, there's a follow-up study by Norbert Hagemann and Jan Leissing, called "Seeing Red." There, the authors ran an experiment to see if referee bias could be the cause of the "red beats blue" effect. They took a bunch of video clips of Tae Kwan Do matches, where one fighter was blue and the other was red. Then, they created duplicates, but electronically switched the colors. They showed the clips to experienced referees, and had the refs score the fights.

Since every clip appears twice, once in each color combination, you'd expect red and blue to score equally. But it turned out that there was indeed a bias in favor of the red combatant. The table/figure is missing from the online version of study, but the authors say that

"The competitor wearing red protective gear was awarded an average of 13% (0.94 points) more than the competitor wearing blue protective gear."

So the average score was 8-7 for the red guy. That seems like a pretty huge advantage (it's significant at .01).

I'm still shocked that this is happening; I didn't expect referees to be so biased. I'm hoping that it's not really true. I'm hoping that what's actually going on is that 100 different researchers tried this experiment, and this was the only one that came up significant at 1%.

But if not, and this is a real effect, well, at least it explains why the Habs have more Stanley Cups than God's Team.

Hat tip: anonymous