Friday, April 25, 2014

The Wisdom of (Little) Crowds

The problem with big groups is this: a faction of the group will follow correlated cues–in other words, the cues that look the same to many individuals. If a correlated cue is misleading, it may cause the whole faction to cast the wrong vote. Couzin and Kao found that this faction can drown out the diversity of information coming from the uncorrelated cue. And this problem only gets worse as the group gets bigger.

Small groups, Kao and Couzin found, can escape this trap. That’s because probability works differently in small groups as opposed to large ones. It’s not unheard of, for example, to roll the same number a few times in a row. But it’s really weird to do so a thousand times in a row. Likewise, in a small decision-making group, a lot of individuals may end up using uncorrelated cues–the ones that give wisdom to crowds.

Couzin and Kao’s analysis, which has just been published in the Proceedings of the Royal Society, doesn’t prove that the wisdom of big crowds is a fatally flawed idea. But it does serve as a warning that even simple factors can have a big impact on how groups make decisions. And it may help to explain how real animals form groups.

When scientists first came to appreciate how groups can make decisions, a question naturally arose: why don’t all animals live in gigantic groups? Some researchers argued that big groups had drawbacks that balanced the advantage they offered in making good decisions.

But Couzin and Kao wonder if such drawbacks don’t, in fact, exist. Perhaps animals live in smaller groups because smaller groups are better at making decisions.

Even the animals that do live in big groups may not actually be solving problems en masse. Only a small fraction of the group may actually be casting votes, while the rest follow their lead.

Couzin and Kao’s work also raises some questions about how we humans make decisions. If people are basing their decisions on the same information, they may be more prone to bad decisions in big groups. All things being equal, smaller groups might do better. And big groups might improve their choices if people avoided relying on the same sources of information.

- Carl Zimmer

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