對一組人員對某事的判斷求平均值，可能是有效的方法。不過，如果讓他們相互展開討論，可能適得其反。KH報道。

If you want to guess how many jelly beans are in a jar, you should ask your friends. Then average their answers. Because a group guess is often more accurate than that of any one individual. Just don’t let them peek at each other’s responses. Because a new study shows that social influence can sway people’s estimates and render the crowd incorrect. The work appears in the Proceedings of the National Academy of Sciences. [Jan Lorenz et al, How social influence can undermine the wisdom of crowds effect]

Crowd wisdom is actually a statistical phenomenon. Gather enough estimates and the wild guesses cancel each other out, bringing you closer to the answer. But psychology and statistics don’t mix. And knowing what your peers think doesn’t make you any smarter.

European scientists asked volunteers to estimate statistics like the population density of Switzerland. Each person got five guesses. Some were shown their peers’ answers and others weren’t. Turns out that seeing others’ estimates led to a lot of second guessing. Which narrowed the range of the group’s responses and pointed them in the wrong direction. Even worse, knowing that others said the same thing made everyone more confident they were right. So there is wisdom in numbers—as long as those numbers keep quiet `til they’re counted.

—Karen Hopkin