Valid demeanor measures would have a significant practical advantage over the polygraph because tests could be conducted noninvasively and even without the examinee’s knowledge. We note but do not judge the significant ethical and legal issues raised by this practical advantage. There is also the potential that interrogators might be taught to improve their skills by becoming more sensitive to demeanor indicators. In our judgment, any systematic effort to improve techniques for detecting deception should include attention to measures of demeanor.
Available evidence does not suggest that any direct investigation method is likely to provide a reasonable and valid alternative to the polygraph. The evidence does suggest ways to improve these techniques. Studies assessing whether they provide incremental accuracy over the polygraph, or whether the polygraph provides incremental accuracy over direct investigation, have not been done.
Our conclusions about specific potential alternatives or supplements to the polygraph are all tentative and made with limited confidence because of the limited base these techniques now have in either basic science or empirical criterion validation. We have much greater confidence in concluding that security and law enforcement agencies need to improve their capability to independently evaluate claims proffered by advocates of new techniques for detecting deception. The history of the polygraph makes clear that such agencies typically let clinical judgment outweigh scientific evidence in their assessment of the validity of techniques for the psychophysiological detection of deception or the detection of deception from demeanor. Although it is probable that belief in a technique can go a long way in making it useful for deterrence and for eliciting admissions, overconfidence does not in the long run contribute positively to national security or law enforcement goals. Agencies that use such techniques should support independent scientific evaluation so that they can be fully informed when making decisions on whether and how to use the techniques and on how to use the test results they produce. We return to this issue in Chapter 8.