accurate if such questions can be asked than if they cannot. In addition, if the target answers to these questions are known only to examiners and to the individuals who are the targets of the investigation or screening, it is possible to use concealed information polygraph test formats or to use other tests that rely on orienting responses, such as those based on brain electrical activity. Thus, polygraph testing in general and concealed information tests (either with the polygraph or other technologies) are more attractive under these conditions than otherwise.

Employee security screening in the DOE laboratory is a situation that is quite unfavorable for polygraph testing in terms of all of the factors just discussed. Other potential applications should be evaluated after taking these factors into account. Polygraph testing is likely to look more attractive for some of these applications, even though in all applications it can be expected to yield a sizable proportion of errors along with the correct classifications.

In this connection, it is worth revisiting the class of situations we describe as focused screening situations. Events occurring since the terrorist attacks of September 11, 2001, suggest that such situations may get increased attention in the future. Focused screening situations differ both from event-specific investigations and from the kinds of screening used with employees in national security organizations. An illustrative example is posed by the need to screen of hundreds of detainees captured in Afghanistan in late 2001 to identify those, perhaps a sizable proportion, who were in fact part of the Al Qaeda terrorist network. Such a focused screening situation is like typical security screening in that there is no specific event being investigated, but it is different in that it may be possible to ask specific relevant questions, including questions of the concealed information variety.6 It is thus possible to use concealed information polygraph tests or other tests that require the same format and that are not appropriate for screening situations in which specific questions cannot be constructed. For example, members of Al Qaeda might be identifiable by the fact that they have information about the locations and physical features of Al Qaeda training camps that is known to interrogators but not to very many other people. Another example might be the screening of individuals who had access to anthrax in U.S. biological weapons facilities to identify those who may be concealing the fact that they have the specific knowledge needed to produce the grade of anthrax that killed several U.S. citizens in the fall of 2001. Again, even though the examiners do not know the specific target action, they can ask some focused relevant questions.

The tradeoffs in focused screening are often very different from those in other screening situations because the base rate of the target activities may lie below the 10 percent or higher typical of criminal investigations



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