To paraphrase from an interesting article, the jelly bean in a jar experiment and predictive markets prove that the power of the crowd will beat even the experts, hence the markets generally are efficient. The exception is when the experts are given too much air time biasing the crowds opinion distorting the cancellation of error in divergent opinions.

Two things this teaches:

1. We should value all opinions
2. The more we know the humbler we should be to this

Adam Robinson contends: 

With respect to the esteemed Mr. Sears, guessing stock prices is nothing like guessing jelly beans.

In the first place, there's a risk associated with markets that does not exist with jelly beans. But more important, in markets the "guesses" of participants influence each other, with all sorts of feedback loops that do not exist at state fairs guessing jelly beans.

It would be interesting to see whether this second factor can be tested in the field: run the counting contest but post each of the guesses, in ranked order, along with high guess, low guess, median guess, average guess for easy overview, and see whether that information influences participants' guesses (for comparison, two groups could be tested, one with access to the information and one without).

A prize and a penalty could also be attached to guesses, and for a further dimension, see whether and how much participants would be willing to have access to the "market" information. 

Russell Sears notes: 

The predictive markets (the markets that predict things like election results, winners of Oscars, etc) do run very close to the proposed modification of the jelly bean test, with the added bonus that the "bettor" must be willing to lose and hence think he has an edge, like the stock markets.

One example is of a multiple choice of one out of four listing of the one not being in the old music group The Monkees. If 7% know all, 5% know two, and 5% know one, and rest don’t have a clue. With all votes random, besides the choices eliminated due to knowledge, it takes a fairly small number of players to get it right. This would work even if the "expert" did not have perfect knowledge, such as the Oscars, or the stock market. 


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