 The posterior probability of a hypothesis given the evidence should not be confused with the strength (or probative value, weight) of the evidence in favor of the hypothesis. The strength of an item of evidence reflects its impact on the probability of the hypothesis. Suppose the prior probability of \(H\) is extremely low, say \(\Pr(H)=.001\), but taking evidence \(E\) into account brings this probability up to 35%, that is, \(\Pr(H \pmid E)=.35\). This is a dramatic upward shift. Even though the posterior probability of \(H\) given \(E\) is not high, \(E\) strongly favors \(H\). This section examines how probability theory helps to assess the strength of evidence.