Response Making Terrorism Risk Analysis Less Harmful and More Useful: Another Try

Although Ezell claims that we only “repackaged in a new article the limitations identified by Ezell et al. of PRA in terrorism risk analysis, ” he neither ad-dresses nor refutes any of our substantive technical points and examples, and his comments reflect a fun-damental lack of understanding of our main ideas. We are therefore grateful for this opportunity to clar-ify our reasoning in light of his comments, as follows. 1. Intelligence analysts cannot condition on knowledge that they do not have. Ezell asserts that we, and the National Research Coun-cil, have overlooked what he calls the “ob-vious fact ” that “intelligence analysts con-sider terrorist knowledge... when assessing probabilities of attack. ” However, a majo