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discusses the use of cost-benefit analysis to provide a common measure.

Recommendation: While human mortality and the magnitude and duration of morbidity should remain the primary focus of DHS bioterrorism risk analysis, DHS should incorporate other measures of societal loss, including the magnitude and duration of first- and second-order economic loss and environmental and agricultural effects.

Methods for Improved Modeling of Intelligent Adversaries

The committee attaches great importance to the realistic representation of the behavior of an intelligent adversary. BTRA probabilities are conditioned on past events and are retrospective, whereas the terrorist is prospective, constantly adjusting tactics to exploit any evident weakness in U.S. defenses.

To offer some concrete examples of how to credibly represent the behavior of an intelligent adversary, the committee presents three ways to represent adversarial decisions: (1) a “bioterrorism decision model” using off-the-shelf software; (2) a tri-level decision support model to allocate defensive investments (visible to the attacker) that represents an attacker’s reasonable response to observing these preparations, and reactions to any attack with the resources made available by the defensive investments; and (3) a game-theoretic model of the adversaries that randomizes expected consequences to capture the variability of outcomes. These are not mere theoretical tools, but rather substantive suggestions drawn from extensive research and experience in the military and in the private sector. These suggestions can significantly improve the credibility and usefulness of the BTRA.

Recommendation: In addition to using event trees, DHS should explore alternative models of terrorists as intelligent adversaries who seek to maximize the achievement of their objectives.

Use of Intelligent-Adversary Risk Analysis Techniques for Other Threat Areas

The committee believes that each of its suggested extensions to realistically represent adversarial behavior is applicable to biological, chemical, and/or radioactive threats. Although distinct models may need to be developed for the analysis of each of these threats, the resulting analyses can be compared on a common consequence scale to suggest and evaluate risk management strategies that encompass all terrorist threats.

Regarding the Use of the BTRA in Its Present Form

For the reasons noted in this report’s recommendations and their justifying text, the committee believes that the BTRA in its present form should not be used to assess the risk of bioterrorism threats. For the same reasons, the committee does not recommend trying to extend the BTRA to the qualitatively different chemical and radioactive threats.

Recommendation: The BTRA should not be used as a basis for decision making until the deficiencies noted in this report have been addressed and corrected. DHS should engage an independent, senior technical advisory panel to oversee this task. In its current form, the BTRA should not be used to assess the risk of biological, chemical, or radioactive threats.

The committee takes very seriously the bioterrorism threats and potential consequences that it has had to consider in this study. It is fully aware of the potential impact of its recommendations on the BTRA of 2008 and the stakeholders who await it. However, it believes that the failure to properly model intelligent adversaries and a continuation on the path of unnecessary complexity in computer modeling and simulations will not help the United States defend against the bioterrorist threats in the 21st century and will not meet the intent of HSPD-10. Therefore, the committee unanimously believes that an improved BTRA is needed to provide a much more credible foundation for risk-informed decision making.


DHS (Department of Homeland Security). 2006. Bioterrorism Risk Assessment. Biological Threat Characterization Center of the National Biodefense Analysis and Countermeasures Center. Fort Detrick, Md.

Office of Homeland Security. 2002. National Strategy for Homeland Security. Available at Accessed November 1, 2006.

The White House. 2004. Homeland Security Presidential Directive 10 [HSPD-10]: Biodefense for the 21st Century. Available at Accessed January 16, 2008.

The White House. 2007. Homeland Security Presidential Directive 18 [HSPD-18]: Medical Countermeasures Against Weapons of Mass Destruction. Available at Accessed January 16, 2008.

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