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This is Scientific American's 60-Second Science. I'm Karen Hopkin. This will just take a minute.

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 peek¹ 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 Proceedings² of the National Academy of Sciences.

Crowd wisdom is actually a statistical³ phenomenon. Gather enough estimates and the wild guesses cancel each other out, bringing you closer to the answer. But psychology⁴ 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 density⁵ 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 pointed⁶ 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 till they're counted.

Thanks for the minute. For Scientific American's 60-Second Science, I'm Karen Hopkin.