ambiguous (e.g., “Have you ever committed a security violation?”). Also, the base rate for deception in this study was quite high (over three-quarters of examinees were confirmed as deceptive on one or more questions); in security and espionage screening, the base rate is likely to be extremely low. For these reasons, generalizing from this study to other screening applications is risky. In addition, determination of truth is problematic for this study because truth was defined by a mixture of criteria, including the search of public records for convictions and bankruptcies, a urine test for marijuana, and, in an unreported number of instances, confession. Truth established by confession may not be independent of the polygraph test. A reasonable guess is that polygraph testing in other kinds of security screening situations will be less accurate than in this one.

We note that although the use of comparison questions is undoubtedly helpful in controlling for such differences, it is a misconception to assume this strategy to be fully effective, for a variety of reasons. For instance, differential electrodermal responses to different stimuli may be especially hard to detect in individuals who are highly reactive or highly nonreactive to all stimuli. We also note that polygraph tests achieve accuracy greater than chance despite the failure of most scoring systems to control for these differences.

This strategy can also be applied to the relevant-irrelevant test. With concealed information tests, however, it can only be used by examinees who have concealed information because only they can distinguish relevant from comparison questions.

The only true screening study we found, which did not meet our standards for inclusion in the quantitative analysis because it did not use a replicable scoring system, yielded an accuracy index of 0.81.