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Clinical Trial
, 14 (11), e0224725

Self-serving Incentives Impair Collective Decisions by Increasing Conformity

Clinical Trial

Self-serving Incentives Impair Collective Decisions by Increasing Conformity

Sepideh Bazazi et al. PLoS One.


The average judgment of large numbers of people has been found to be consistently better than the best individual response. But what motivates individuals when they make collective decisions? While it is a popular belief that individual incentives promote out-of-the-box thinking and diverse solutions, the exact role of motivation and reward in collective intelligence remains unclear. Here we examined collective intelligence in an interactive group estimation task where participants were rewarded for their individual or group's performance. In addition to examining individual versus collective incentive structures, we controlled whether participants could see social information about the others' responses. We found that knowledge about others' responses reduced the wisdom of the crowd and, crucially, this effect depended on how people were rewarded. When rewarded for the accuracy of their individual responses, participants converged to the group mean, increasing social conformity, reducing diversity and thereby diminishing their group wisdom. When rewarded for their collective performance, diversity of opinions and the group wisdom increased. We conclude that the intuitive association between individual incentives and individualist opinion needs revising.

Conflict of interest statement

The authors have declared that no competing interests exist.


Fig 1
Fig 1. Schematic of the experiment design and operationalisations.
At the start of each trial, groups were told if the trial was in the collective or individual payoff condition. Then on the central display, a map of London was presented for five seconds. A question relating to a location in London was also shown above the map and read aloud by the experimenter. The map disappeared and participants were prompted to provide their first answer, Response 1, by moving their dot on their device’s screen to give their answer. Then the map and question were displayed again for five seconds, and the question was read out loud once more. During this time participants were not permitted to move their dots. In the trials where social information was present, a star representing the position of the group’s mean Response 1 was additionally displayed on the map. Participants were then asked to provide their final answer, Response 2. Finally, the correct answer was revealed. In individual payoff condition trials, participants were informed with a feedback message on their mobile device whether their dot was in the same grid location as the correct answer. In collective payoff condition trials, participants were able to see the group’s mean Response 2 position on the shared display. A video of an example trial is available in SI (S1 Video). Example responses illustrate how group diversity and group error were operationalised. For group diversity, this was the distance between with group's mean position at Response 1, and their individual responses at Response 2. Group error was operationalised as the distance between the group mean response at Response 2 and the correct answer.
Fig 2
Fig 2. Group diversity and group error.
Analysis and example response data in individual (top row) and collective (bottom row) conditions. In the left column, participants' responses to an example question: 'where do most Korean people live in London?' are shown by small dots. This trial was from the social information present condition. Dots are coloured by groups and lines join them to the group mean response, shown as a large dot. Group diversity is analysed in the centre column, and group error on the right (all questions and trials). In each density plot, solid lines show the distributions of our data when social information is present (yellow) and absent (blue), with means given by dotted lines. These distributions highlight group diversity and error for individual and collective pay-off groups; when rewarded for the accuracy of their individual responses, participants converged to the group mean, displaying reduced group diversity and increased group error. To the right of each data distribution, grey lines show the Bayesian posterior distribution for the difference between social information conditions within each payoff condition, with the 95% credibility intervals shaded in grey.

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