Can a crowd of ordinary people guess better than the experts?

Often, yes: for the right kind of question, the combined guess of many ordinary people can beat the judgment of a single expert. This is called the wisdom of the crowd, the idea that the collective opinion of a diverse and independent group yields the best judgement.

The classic story comes from 1906. The statistician Francis Galton visited a livestock fair where villagers were invited to guess the weight of an ox after it had been slaughtered and dressed. Nearly 800 people took part. Galton studied their entries afterwards and found that the median guess, 1207 pounds, was within 1 percent of the true weight of 1198 pounds. He called the middlemost estimate the vox populi, the voice of the people.

Why does this work? Every person's guess contains some random error: one is too high, another too low. When you take the average of many answers, those individual errors tend to cancel out and the noise is tempered. The crowd is not clever in any mystical way. It is just that its mistakes point in different directions.

That is also the catch. If everyone is pushed the same way, nothing cancels. Averaging fixes random errors, but not errors that affect the whole crowd in the same way. A crowd works best when people think for themselves and the question has a real answer.