The Condorcet Jury Theorem and the wisdom of informed groups

The probability that a group of people will arrive at a correct answer to a factual question increases toward 100 percent as the size of the group increases. This is the Condorcet Jury Theorem, as explained in Cass R. Sunstein, Infotopia: How Many Minds Produce Knowledge (Oxford 2006) at 25, which holds true so long as a few restrictions are satisfied. One is that the people in the group must be independent, which means that they mustn’t influence each other’s opinions; they must be unbiased; most of them must be well-informed enough to have a better than 50:50 chance of getting the correct answer; and the actual answer must be known. These restrictions come from Len Fisher, The Perfect Swarm: The science of complexity in everyday life (Basic Books 2009) at 78-79.

If your law department has a lawyer conference and each lawyer is more likely than not to be correct about a fact, even if ever so slightly, the majority answer when submitted independent will be close to correct. For example, if the question were the average cash bonus awarded the previous year, and most of the lawyers have a sense of that figure, the resulting collective estimate will come very close.

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