 As is apparent from Bayes’ theorem, multiplying the prior probability by the Bayes factor yields the posterior probability \(\Pr(H \pmid E)\). Other things being equal, the lower the prior probability \(\Pr(H)\), the lower the posterior probability \(\Pr(H \pmid E)\). The base rate fallacy consists in ignoring the effect of the prior probability on the posterior (Kahneman and Tversky 1973). This leads to thinking that the posterior probability of a hypothesis given the evidence is different than it actually is (Koehler 1996).