Expert Judgement in Terrorism Risk Assessment

Since 9/11, the probabilistic risk assessment of losses from terrorism has formed a quantitative basis for informed terrorism risk management. An irreducible element is the elicitation of expert judgement. In any application domain, the reliance on expert judgement can be minimized through the establishment of core conceptual principles, such as economic game theory and adversarial risk analysis, which govern the risk phenomena under consideration. For non-state threat actors, such as the Jihadi groups, Al Qaeda and ISIS, their limited logistical resources compared with western counter-terrorism intelligence and law enforcement capacity, greatly constrain the spectrum of their operations, which can be modelled quite reliably in a probabilistic manner. However, state-sponsored terrorism poses a much more severe challenge, especially in connection with the use of weapons of mass destruction, such as nuclear and chemical weapons. In this paper, the fundamental principles of terrorism risk assessment are reviewed, and the use of expert judgement is illustrated in relation to state-sponsored nuclear and chemical weapon deployment.