No effect of blue on winning contests in judo

Proceedings of the Royal Society B: Biological Sciences, May 2008

A study by Rowe et al. reported a winning bias for judo athletes wearing a blue outfit relative to those wearing a white one during the 2004 Olympics. It was suggested that blue is associated with a higher likelihood of winning through differential effects of colour on opponent visibility and/or an intimidating effect on the opponent. However, we argue that there is no colour effect on winning in judo. We show that alternative factors, namely allocation biases, asymmetries in prior experience and differences in recovery time are possible confounding factors in the analysis of Rowe et al. After controlling for these factors, we found no difference in blue and white wins. We further analysed contest outcomes of 71 other major judo tournaments and also found no winning bias. Our findings have implications for sports policy makers: they suggest that a white–blue outfit pairing ensures an equal level of play.

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No effect of blue on winning contests in judo

Peter D. Dijkstra () 1 2 3 Paul T. Y. Preenen 0 2 0 Group of Work and Organizational Psychology, University of Amsterdam , 1018 WB Amsterdam , The Netherlands 1 Behavioural Biology Group, University of Groningen , PO Box 14, 9750 AA Haren , The Netherlands 2 and Evolutionary Biology, Graham Kerr Building, Faculty of Biomedical and Life Sciences, University of Glasgow , Glasgow G12 8QQ , UK 3 Division of Environmental and Evolutionary Biology, Graham Kerr Building, University of Glasgow , Glasgow G12 8QQ , UK A study by Rowe et al. reported a winning bias for judo athletes wearing a blue outfit relative to those wearing a white one during the 2004 Olympics. It was suggested that blue is associated with a higher likelihood of winning through differential effects of colour on opponent visibility and/or an intimidating effect on the opponent. However, we argue that there is no colour effect on winning in judo. We show that alternative factors, namely allocation biases, asymmetries in prior experience and differences in recovery time are possible confounding factors in the analysis of Rowe et al. After controlling for these factors, we found no difference in blue and white wins. We further analysed contest outcomes of 71 other major judo tournaments and also found no winning bias. Our findings have implications for sports policy makers: they suggest that a white-blue outfit pairing ensures an equal level of play. 1. INTRODUCTION Certain colours, like red and orange, are sexually selected traits signalling male quality, aggression and dominance in a wide variety of organisms (e.g. Rowland 1989; Pryke et al. 2001; Maan et al. 2004; reviewed in Andersson 1994; Hill & McGraw 2006). In aggressive interactions, these colours may increase the likelihood of winning (Evan & Norris 1996; Baube 1997; Cuthill et al. 1997; Dijkstra et al. 2005; Pryke & Griffith 2006). This winning bias has traditionally been attributed to the inherently intimidating effect of red coloration on opponents. Interestingly, Hill & Barton (2005) reported a similar effect in human combat sports; they found that wearing of a red outfit was associated with a higher winning probability relative to wearing a blue outfit in the mens division of Greco-Roman wrestling, freestyle wrestling, boxing and tae kwon do. Recently, Rowe et al. (2005) proposed the idea that this effect is not unique for red coloration. They found in another human combat sport, judo, a significant winning bias for athletes wearing a blue outfit ( judogi ) compared with those wearing a white judogi during the 2004 mens Olympics. Here we argue that there exists no winning bias for blue and that their findings were confounded. Two, not mutually exclusive, mechanisms have been proposed to underlie the winning bias for blue. First, Rowe et al. (2005) attribute the effect to blue and white colour having differential effects on opponent visibility. The white judogi may be more visible than the blue judogi, allowing the athlete in blue to better anticipate the movements of his (white) opponent. A second explanation was given by Barton & Hill (2005). They suggested that blue coloration is brighter than white, and may therefore have an intimidating effect on opponents, as was originally proposed for red coloration. Both explanations are unlikely. Considering the first explanation, we believe that a differential perception effect is unlikely to occur in a situation where athletes fight at close quarters in brightly lit areas, as in judo (see Barton & Hill 2005). Considering the second explanation, inherently intimidating effects of colour on opponents have been suggested for red coloration in a wide range of animal species (e.g. Dijkstra et al. 2005; Pryke & Griffith 2006) but never for blue coloration. For example, in a non-human primate, the intensity of red coloration on the nose correlated with dominance status (Setchell & Wickings 2005). In humans, anger may trigger increases in facial blood flow (Drummond 1999). In people with a fair skin, this facial reddening may alter the behaviour of others in social encounters (Drummond & Quah 2001). Therefore, the traditional intimidating nature of red coloration may influence dominance in humans (Hill & Barton 2005). Such an effect cannot be logically attributed to blue coloration. We argue that athletes wearing a blue judogi are not more likely to win than those wearing a white judogi, and suggest that the results obtained by Rowe et al. (2005) were compromised by three confounding factors: (i) seeding system, (ii) inclusion of repechage rounds, and (iii) differences in recovery time. First, wearing of judogi colour was not completely determined at random during the 2004 Olympics, even though athletes switch blue and white judogi depending on their position in the tournament bracket (electronic supplementary material). Top-ranked athletes were seeded so as to avoid matching them against one another before the semi-finals; seeded athletes (...truncated)


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Peter D Dijkstra, Paul T.Y Preenen. No effect of blue on winning contests in judo, Proceedings of the Royal Society B: Biological Sciences, 2008, pp. 1157-1162, 275/1639, DOI: 10.1098/rspb.2007.1700