Learning Through the Grapevine: The Impact of Message Mutation, Transmission Failure, and Deliberate Bias

38 Pages Posted: 7 Dec 2018 Last revised: 24 Jun 2019

See all articles by Matthew O. Jackson

Matthew O. Jackson

Stanford University - Department of Economics; Santa Fe Institute; Canadian Institute for Advanced Research (CIFAR)

Suraj Malladi

Stanford University, Graduate School of Business

David McAdams

Duke University - Fuqua School of Business

Date Written: March 1, 2019

Abstract

We analyze whether learning is simply difficult or impossible when first hand information is relayed to agents through long chains of noisy person-to-person communication. Suppose noise only takes the form of random mutations and message dependent transmission failures. Agents can still learn but at the cost of accessing many more chains of communication. They learn fully when they have more than a certain threshold number of chains and learn nothing with fewer. On a positive note, this threshold remains unchanged when agents adopt a simpler, naive learning rule. In particular, both the frequency and content of their communications are informative about the state, but agents can safely restrict attention to the more important of these dimensions. Results change dramatically when there are biased agents who relay their preferred message despite what they hear. Learning is typically impossible in the presence of even an arbitrarily small fraction of biased agents. This can explain why people become stuck at potentially different priors, despite a significant body of primary evidence pointing to one answer (e.g., disagreement on the effects of vaccination or the reality of global warming). We show that a planner can recover partial learning by limiting the number of contacts to whom agents can pass along a given message, a policy some messaging platforms are starting to use.

Keywords: Social Learning, Communication, Noise, Mutation, Bias, Fake News

JEL Classification: D83, D85, L14, O12, Z13

Suggested Citation

Jackson, Matthew O. and Malladi, Suraj and McAdams, David, Learning Through the Grapevine: The Impact of Message Mutation, Transmission Failure, and Deliberate Bias (March 1, 2019). Available at SSRN: https://ssrn.com/abstract=3269543 or http://dx.doi.org/10.2139/ssrn.3269543

Matthew O. Jackson (Contact Author)

Stanford University - Department of Economics ( email )

Landau Economics Building
579 Serra Mall
Stanford, CA 94305-6072
United States
1-650-723-3544 (Phone)

HOME PAGE: http://www.stanford.edu/~jacksonm

Santa Fe Institute

1399 Hyde Park Road
Santa Fe, NM 87501
United States

Canadian Institute for Advanced Research (CIFAR) ( email )

180 Dundas Street West, Suite 1400
Toronto, Ontario
Canada

Suraj Malladi

Stanford University, Graduate School of Business ( email )

Stanford, CA
United States

David McAdams

Duke University - Fuqua School of Business ( email )

Box 90120
Durham, NC 27708-0120
United States

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