Updating Prior Beliefs Based on Ambiguous Evidence

AbstractThis paper investigates a problem where the solver must firstly determine which of two possible causes are the source of an effect where one cause has a historically higher propensity to cause that effect. Secondly, they must update the propensity of the two causes to produce the effect in light of the observation. Firstly, we find an error commensurate with the ‘double updating’ error observed within the polarisation literature: individuals appear to first use their prior beliefs to interpret the evidence, then use the interpreted form of the evidence, rather than the raw form, when updating. Secondly, we find an error where individuals convert from a probabilistic representation of the evidence to a categorical one and use this representation when updating. Both errors have the effect of exaggerating the evidence in favour of the solver’s prior belief and could lead to confirmation bias and polarisation.

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