Abstract

Psychological studies show that the beliefs of two agents in a hypothesis can diverge even if both agents receive the same evidence. This phenomenon of belief polarisation is often explained by invoking biased assimilation of evidence, where the agents’ prior views about the hypothesis affect the way they process the evidence. We suggest, using a Bayesian model, that even if such influence is excluded, belief polarisation can still arise by another mechanism. This alternative mechanism involves differential weighting of the evidence arising when agents have different initial views about the reliability of their sources of evidence. We provide a systematic exploration of the conditions for belief polarisation in Bayesian models which incorporate opinions about source reliability, and we discuss some implications of our findings for the psychological literature.

Highlights

  • Suppose two people, call them Alice and Bob, are members of a jury that has been appointed in order to decide on whether the defendant in a murder case is guilty

  • We find that belief polarisation is not possible on the hypothesis in such models given only one piece of evidence

  • We have considered the question of whether beliefs about reliability of sources of information may play a role in driving belief polarisation

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Summary

Introduction

Call them Alice and Bob, are members of a jury that has been appointed in order to decide on whether the defendant in a murder case is guilty. During the trial Alice and Bob are confronted with a number of pieces of evidence which tell either in favour or against this hypothesis They see a police report that a weapon such as was used in the murder was found in the defendant’s house. This constitutes positive evidence for the hypothesis that the defendant is guilty They see forensic evidence which shows that the DNA traces left on the body do not match the DNA of the defendant.

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