Overall Assessment

Theoretically, it should be possible to detect deception from demeanor with some skill. And evidence from experimental and field studies has identified some cues emitted by people who are deceptive, particularly in high-stakes situations, that can be observed with human sense organs. Moreover, a small proportion of experienced interviewers exhibit skill in detecting deception from such cues. However, attempts to systematize such skill have so far been disappointing. Voice stress analysis and graphology, two commonly used techniques, have not convincingly demonstrated accuracy for detecting deception.

The gap between the promise and the practice of the detection of deception from demeanor has several possible explanations. It may be that different liars emit different cues, so that any standard protocol would have only limited accuracy. It may also be that research has not yet identified the most valid behavioral indicators of deception. The research has seemed to focus mostly on particular channels (e.g., facial expression, voice quality) rather than on developing an underlying theory of behavioral indicators or searching for several indicators, possibly including disparate channels, that have high accuracy in situations of interest. It seems possible that such approaches could lead to methods of detecting deception from demeanor with practical value. It is also possible that such methods might add information to what can be achieved by physiological indicators—though that possibility has not to our knowledge been investigated. In our judgment, the search for useful methods of detecting deception should not exclude efforts to find valid indicators in the subtleties of behavior.


Methods of direct investigation, such as background checks, interviews, and the like are already used for making personnel decisions, both with and without the polygraph as accompaniment. This section reviews what is known about the ability of these techniques to detect individuals who pose risks to their employers’ objectives.

Background Checks

Little scientific evidence is available about the validity of the background checks and other investigative methods that have been used to identify individuals who create threats to national security. There is some anecdotal evidence, however, on the value of these methods. Publicly available reports indicate that the spies who have been detected within

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