Applying the General Theory of Quantitative Risk Assessment (QRA) to Terrorism Risk

The purpose of this paper is to point out that the general theory of quantitative risk assessment (QRA) applies perfectly well to evaluating and quantifying the risk from terrorism. The main difference occurs during the "scenario identification" part of the risk assessment process. Whereas, in an "ordinary" QRA, we ask the question, "What can go wrong?," in terrorism risk assessment (TQRA) we ask, "If I wanted to, what could I make go wrong?" In answering this new question, the Theory of Scenario Structuring and the use of fault and event trees play the major roles as before. Also, the concept of "resources" now moves to center stage as part of the process of identifying terrorism scenarios. So also does the use of Bayes' theorem, not only to assess a priori the likelihoods of specific terrorism scenarios, but also as a crucial part of surveillance systems that have, potentially, the ability to quantify the likelihoods that such scenarios are in process.