 In the examples considered so far, probabilities were assigned on the basis of empirical frequencies and expert opinions. For example, an expert testimony that only 5% of people possess a particular blood type was used to set \(\Pr(\match \pmid \neg \source)=.05\). Probabilities were also assigned on the basis of common sense, for example, \(\Pr(\match \pmid \source)\) was set to 1 assuming that if someone is the source of the crime traces, the person must match the crime traces (setting aside the possibility of framing, fabrication of the traces or false negatives in the test results). But probabilities need not always be assigned exact values. Agreeing on an exact value can in fact be extremely difficult, especially for prior probabilities. This is a challenge for legal probabilism (see later in  §7.3).  One way to circumvent this challenge is to avoid setting exact values and adopt plausible intervals. This method is based on sensitivity analysis, an assessment of how prior probabilities affect other probabilities.