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Big Groups Reach Better Decisions Faster

Posted By Prucia Buscell, Thursday, March 31, 2011
Updated: Friday, April 1, 2011
Big Groups Reach Better Decisions Faster Even When Swimming 

Internet search engines, Wikipedia, financial markets, and internet communities are known to make use of the wisdom of the crowd. It seems humans aren't the only creatures with that ability. Even fish have it.    

Researchers have found that large shoals of fish make decisions better and faster than small shoals. A story in Nature by Larissa Conradt reports on an experiment in which researchers gave groups of mosquitofish a choice between a route that went past a model predator and one that was free of such danger. The larger the shoal of fish, the more likely they were to pick the safe route, and the faster they decided.

Dr. Ashley J. W. Ward, a senior research fellow at the University of Sydney in Australia, and colleagues,  assert in "Fast and accurate decisions through collective vigilance in fish shoals," published in the Proceedings of the National Academy of Sciences, that large shoals achieve greater efficiency in decision making not only because of effective communication, but because of division of labor. While a single fish would have to scan its entire environment to detect danger, fish in groups can focus their information gathering to a smaller area. The researchers didn't find individual predator-detection differences among the fish, so group diversity seems not to explain superior group performance. The authors suggest in a large group there is greater likelihood that a fish will detect a predator by chance and communicate that information very quickly to nearby fish. They proposed the better performance is "facilitated by a form of self-organized vigilance, whereby information acquired by one individual is transmitted by positive feedback and communicated across the group."

The Nature story says both speed and accuracy were probably influenced by the way information is communicated. Pairs of fish within six centimeters of each other reacted rapidly to each other's movement changes, and a fish's choice of route depended on the average choice of fish nearby. Researchers cite two important features of this "simultaneous self-organized system of communication:" The speed of information exchange is high, and communication is decentralized, so that  information transfer can start with any individual in the shoal.

The Nature article warns that collective decisions aren't always the best. When the decision makers have widely varying abilities, "expert" advice can help. Information cascades can amplify shared misconceptions. And when decision makers want different outcomes, shared decision making might support a factional solution rather than a consensus. Still, researchers want to learn more about how all animals make decisions. 

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