Deliberation increases the wisdom of crowds
The aggregation of many independent estimates can outperform the most accurate individual judgment. This centenarian finding, popularly known as the 'wisdom of crowds', has recently been applied to problems ranging from the diagnosis of cancer to financial forecasting. It is widely believed that the key to collective accuracy is to preserve the independence of individuals in a crowd. Contrary to this prevailing view, we show that deliberation and discussion improves collective wisdom. We asked a live crowd (N=5180) to respond to general knowledge questions (e.g. the height of the Eiffel Tower). Participants first answered individually, then deliberated and made consensus decisions in groups of five, and finally provided revised individual estimates. We found that consensus and revised estimates were less biased and more diverse than what a uniform aggregation of independent opinions could achieve. Consequently, the average of different consensus decisions was substantially more accurate than aggregating the independent opinions. Even combining as few as four consensus choices outperformed the wisdom of thousands of individuals. Our results indicate that averaging information from independent debates is a highly effective strategy for harnessing our collective knowledge.