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When the wisdom of the crowd turns negative

Posted on 13 October 2020

In a new article in Management Science, EUI Chair in Sociology Professor Arnout van de Rijt studies group decisions.

Teams, juries, electorates, and committees must often choose from various alternatives what they judge to be the best option. Condorcet’s famous jury theorem tells us that group decisions based on plurality voting (or relative majority) can be surprisingly wise. Recent experimental studies show this "wisdom of the crowd" is further enhanced if individuals in a group that needs to make a decision can revise their initial votes after seeing those of everyone else.


EUI's Professor Arnout van de Rijt and Dr. Vincenz Frey of the University of Groningen delved further into this positive effect of social information. Their laboratory experiments put groups of 10-14 participants in front of a computer to answer 30 A-or-B questions.

“Our experiments show that the positive effect of social information turns negative if group members do not first contribute an independent vote, but instead cast their votes sequentially such that early mistakes can cascade across strings of decision makers. Just like the jurors in the movie ‘12 Angry Men’, our subjects copied the wrong judgments given by those before them.” said Professor van de Rijt.

“Our findings contribute to a better understanding of the mechanisms behind group decisions and are relevant across disciplines.”

The experiments show that when participants sequentially state which of two answers they deem correct, majorities are more often wrong.

As predicted by the researchers' theoretical model, this happens even though the use of social information on average improves the accuracy of participants' individual votes. In a second experiment van de Rijt and Frey conducted over the internet they increased the number of subjects all answering the same question to 100. They found that if the question was easy, early mistakes were eventually corrected. Conversely, if the first couple of subjects got a difficult question wrong, that early and mistaken majority was never corrected, not even after 100 subjects.


Social Influence Undermines the Wisdom of the Crowd in Sequential Decision Making, Management Science, October 2020