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FIGURE D.1 BTRA modeling alternatives. This figure provides a bioterrorism risk assessment modeling alternative generation table (Parnell, Driscoll, and Henderson, 2008) to help identify the BTRA modeling alternatives available to DHS. The column headings are the modeling decisions that must be made by DHS. The column cells identify the modeling techniques we considered for each modeling decision. The gray shading depicts the committee’s understanding of 2006 BTRA methodology.


Based on the committee’s assessment, several improvements are needed. First and foremost, the methodology must consider the terrorist as an intelligent adversary that will select the best attack strategy to maximize their strategic objectives. Second, the methodology must be transparent. A key goal should be the use of commercially available software that has built-in sensitivity analysis features to improve understanding and transparency. The method should eliminate unnecessary complexity and demands for data that will have no meaning if one bioterrorism attack is made on the United States, e.g., the attack frequency for each agent. Finally, the methodology should be easily modified to support the analysis of risk management alternatives.

Decision analysis offers the potential to make many of the improvements we have discussed. Decision analysis is closely related to probabilistic risk analysis (Paté-Cornell and Dillon, 2006). Single objective decision analysis with decision trees has been used since 1968 (Raiffa, 1968; Clemen, 1996). Multiple objective decision analysis has been used since 1976 (Keeney and Raiffa, 1976; Kirkwood, 1997). Maxwell (2006) summarizes the large selection of commercially available decision and risk analysis software.

Figure D.2 uses the format of Figure D.1 and shows the modeling techniques that would be used in a decision analysis method. The darker shaded cells define one potential decision analysis method used to maximize the achievement of terrorist objectives. The lighter shaded cells describe alternative decision analysis methods. The goal would be to use commercially available tools and keep the models small enough to have reasonable run times. Using commercially available software helps make the models transparent and allows the use of standard decision analysis and sensitivity analysis that provide insights and improve transparency. The decision tree would model the terrorist’s decision to use biological agents to achieve his or her strategic objectives by maximizing consequences to the United States. All of the terrorist decisions would be modeled as decision nodes.

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