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04.04.2017 | Social Contagion: When Do We Spread Other People’s Opinions?

Study Shows that Distance to the Source Plays an Important Role


Everybody does it, whether on- or offline: We share our opinions with our social networks. But which factors determine whether people adopt the opinions of others and spread them further? A new study conducted at the Max Planck Institute for Human Development and Charité – Universitätsmedizin Berlin could provide answers.

Whether or not we believe other people, adopt their opinions, and spread those ideas further depends on many social factors. It is more likely if we hear the same opinion from different sources or if we like the people concerned because we think they are similar to us. But which other factors lead to some opinions and judgments spreading faster and further than others? Researchers at the Max Planck Institute for Human Development and Charité – Universitäts­medizin Berlin have addressed this question in a recent study. Their findings have been published in the journal Proceedings of the National Academy of Sciences (USA).

The researchers investigated under which conditions a person‘s judgments spread to others, how repeated interaction affects this form of social influence, and how far a judgment can travel down a communication chain. They developed two simple experiments, which they ran with a total of 100 participants who did not know each other. In both experiments, participants completed 15 rounds of the same visual perception task in interaction with a randomly chosen partner. The task was to gauge the direction in which the majority of 50 dots on a computer screen were moving. Each participant was seated at a separate computer.

In each round, both partners—called A and B in the first experiment—were asked for an estimate. Participant A went first, and participant B had the opportunity to compare his or her estimate with that of A and to revise it. Round after round, B could learn whether A was performing better or worse at the task. The researchers influenced the performance level by implementing various levels of difficulty. In other words, the pairs were asked to provide the same information, but under different difficulty conditions. “One of the conditions was set up so that the first person in each chain was the better judge, allowing us to see what happened when participant B was able to observe over several rounds that participant A‘s judgment was consistently better than his or her own,” says Mehdi Moussaïd, lead author of the study and researcher in the Center for Adaptive Rationality at the Max Planck Institute for Human Development.

In each round, A’s influence on B’s judgment was measured. The results show that one person‘s influence on another increases as they get to know each other better. “The participants tended to ignore their partner’s estimate at first, but after several interactions they were strongly influenced by it,” says Mehdi Moussaïd. But that was only the case if the originator of the judgment performed consistently better than the receiver. It also emerged that participants evaluated their partner’s errors as being more serious than their own.

In the second experiment, the researchers investigated the dynamics of judgment propagation across several people. The set-up was the same as in the first experiment, but now involved a chain of six participants, each of whom interacted repeatedly with their predecessor. The first person in the chain had the advantage of being allocated tasks with the lowest difficulty level. The researchers were thus able to observe how far participant A’s judgment traveled down the chain. Their findings showed that A’s judgment not only affected B—it also had a significant impact on the judgment of participants C and D, who were not in direct contact with A. However, the influence was no longer detectable after more than three people in the chain.

“In a follow-up simulation, we were able to show that the influence fades across social distance due to a combination of information distortion and the tendency to overweight other people’s errors. Both led to time delays and ultimately to a loss of influence. Nevertheless, it’s remarkable that people can have a considerable influence not only on the judgment of their friends, but also on the judgment of their friend’s friends and of their friend’s friend’s friends,” says Mehdi Moussaïd. “Our findings contribute to the general understanding of social contagion processes. We were able to show that people’s judgments can spread beyond their direct contacts—like the propagation of an infectious disease.”

Contact: 

Public Relations Department
Kerstin Skork
Telefon: 030-82406-211
E-Mail: skork [at] mpib-berlin [dot] mpg [dot] de

Nicole Siller
Telefon: 030-82406-284
E-Mail: siller [at] mpib-berlin [dot] mpg [dot] de

Further information: 

Original Publication
Moussaïd, M., Herzog, S., Kämmer, J., & Hertwig, R. (2017). Reach and speed of judgment propagation in the laboratory. Proceedings of the National Academy of Science. doi:10.1073/pnas.1611998114

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