Comparing the responses of participants in reasoning experiments
to the normative standard of Bayes’ Theorem has been
a popular empirical approach for almost half a century. One
longstanding finding is that people’s belief revision is conservative
with respect to the normative prescriptions of Bayes’
Theorem, that is, beliefs are revised less than they should be.
In this paper, we consider a novel explanation of conservatism,
namely that participants do not perceive information
provided to them in experiments as coming from a fully reliable
source. From the Bayesian perspective, less reliable evidence
should lead to more conservative belief revision. Thus,
there may be less of discrepancy between normative predictions
and behavioural data than previously assumed