study generally focuses on terrorist incidents that involve serious consequences measured by both “hard” and “soft” variables. Hard variables quantify large numbers of injuries and deaths and extensive and costly damage to property; soft variables may include widespread disruption of society’s key functions, loss of public confidence in government’s ability to provide protection against assault, pervasive injury to the population’s way of life and overall peace of mind, and erosion of the economic health of the nation.

The anthrax attacks present a vivid illustration of soft variables. While the number of casualties was modest, the emotional, psychological, and economic impacts were enormous. Hard variables, of course, would have made the situation far worse (imagine if the killers had instead chosen to attack with an agent that causes a deadly contagious disease like smallpox). Nonetheless, the cumulative effect on the nation of a systematic series of small but repeated attacks can be significant.

In addition to assessing the consequences of a particular act of terrorism, we must of course also take into account its likelihood; the product of likelihood times severity of consequence helps us determine how much cost and disruption society should accept in the effort to combat it. One indicator of likelihood is the ease with which the act may be accomplished. Does it require many terrorists working together, or will just one person suffice? Does it involve the complicity of an insider—a nuclear reactor operator, say, or a computer network administrator—who is part of the conspiracy? Does the scale of the effort entail a large expenditure of funds, complex organization, or sophisticated technology that only a nation-state or an established terrorist network could assemble? Or is it simple enough that someone could undertake it in his or her garage?

Phases of Response

In responding to the threat of terrorism, the United States needs a multifaceted approach. This includes the following capabilities, organized according to a time line that extends from before a hypothetical terrorist incident to its aftermath:

  • Intelligence and surveillance involve the observation of persons, groups, and motives—a delicate matter—as well as of potential means of destruction, such as nuclear materials, toxic chemicals, and biological agents.


noncombatant targets by subnational groups or clandestine agents, usually intended to influence an audience.” From p. xvi of Patterns of Global Terrorism 2001, released May 21, 2002, and available online at <>. Meanwhile, the Department of Defense defines terrorism as “the calculated use of violence or threat of violence to inculcate fear; intended to coerce or to intimidate governments or societies in the pursuit of goals that are generally political, religious, or ideological.”

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