Determining the truth is important, but also difficult in many situations. The North American Polygraph (NAP) or "lie detector" offers a tempting technology for such situations. It is popular in North America (and Israel) just as the reading of entrails used to be in ancient Rome, despite the pitfalls of that superstitious procedure.
The North American Polygraph as Entrails Reading:John J. Furedy
Truths and Practical Advice to Potential Users and Victims
Department of Psychology
University of Toronto
The use of the polygraph is, purportedly, a scientifically-based application of psychophysiology. Psychophysiology is an area of psychology that employs subtle changes in physiological functions (like skin resistance, heart rate, and blood pressure) controlled by the autonomic nervous system to differentiate among psychological states. These functions are neither under precise voluntary control nor normally detectable by person in whom they occur.
A polygraphic application, as it is used in North America, includes measurement of physiological functions and a "post-test interview" phase, which is really an interrogation. Its proponents claim that a polygraphic examination can determine from the measurement results alone whether an individual is telling the truth or being deceptive. Reduced to its essentials, the measurement aspect of the polygraph consists of determining whether the autonomically-controlled responses (e.g., skin resistance response or GSR) to questions related to the issue being investigated (e.g., did you steal the money?) are larger than those to so-called "control" questions (e.g., did you do anything you were ashamed of?). So this approach is also commonly called the "Control Question Test" or CQT, because the "test" involves comparing responses to the "control" questions are with those to the relevant (issue-related) questions.
The CQT is, in fact, not a test at all in the sense that, say, an IQ test is a test. IQ tests are controversial in terms of their validity (i.e., how accurately they measure intelligence), but they are scientifically-based and are standardized procedures with a predetermined length and set of questions, which is to say that the test given by one competent operator is essentially the same as that given by another. In contrast, the so-called "control" questions of the CQT are constructed by the examiner as a result of a discussion with the examinee, the entire procedure's duration can vary from 1 to more than 12 hours, and, at the examiner's discretion, a significant and variable (at the examiner's discretion) amount of time can be spent not on its detection function (i.e., determining whether deception has occurred) but on its other interrogatory function (i.e., eliciting a confession of guilty from the examinee).
I used to compare the CQT to tea-leaf reading, but that's a poor analogy, as tea-leaf reading has never been an official procedure. A better comparison is to the reading of entrails which, when done by expert priests, was taken very seriously by the ancient Romans. Entrails reading was a very complex procedure for predicting important future outcomes (like battles), and no self-respecting Roman general made military decisions without consulting the entrails-reading augurs. Nor did other leaders in Roman society hesitate to refer to entrails reading as a way to predict the future. Similarly, in North America, the polygraph is all too readily referred to whether the truth concerns some specific act (like the identity of a killer or rapist) or even some much less clear-cut issue (like whether Clarence Thomas sexually harassed Anita Hill over a decade before the date of the Senate investigation).
The above home truths are stated briefly and dogmatically. More details in support of my arguments may be found in my polygraph-related papers and book on my web page.
Those writings also form the basis of some practical advice to potential users and victims of the CQT polygraph. Among the potential users are lawyers and executives of both security agencies and other businesses like banks, stores, and facilities for young offenders.
For lawyers, the best initial advice is not to use the polygraph. This advice is especially relevant for defence lawyers in criminal cases, but also goes for both sides in civil cases. Once you use the polygraph, you have given implicit assent to a procedure which has no reasonable scientific rationale, and is also contrary to common-sense logical principles. However, if you or your client has made the mistake of using the polygraph, and especially if your client has provided the polygrapher with a confession, then you need to consult an expert who is familiar with elementary principles of psychology (including that of psychological testing) and of psychophysiology, and who is prepared to treat the CQT as an entrails-reading device. Avoid experts who prefer to argue about the CQT's general "accuracy," because this is totally dependent on the examiner as well as the examiner-examinee relationship.
For executives of security organizations, although using the polygraph may be tempting, you should resist the temptation. The repeated use of the polygraph (e.g., annual testing of employees) is particularly dangerous. Even if the polygraph were about 90% accurate (which it is not), an honest individual who was "tested" three times would have about a 30% chance of being classified as "deceptive" once, and that's all it would take to ruin that individual's career. Do you really want to subject your team of workers to this sort of unfairness? Why should they trust you if you're prepared to perpetrate this sort of injustice on them?
The same applies to executives of other businesses. Use of the polygraph may seem reasonable in the short run, but in the long run it leads to distrust up and down the line. Remember that if you use the polygraph, your boss may decide to do so also.
For potential victims of injustice (examinees), the optimal way to combat the polygraph is to refuse to take it. However, there are contexts, especially in the working world in North America (and Israel), where you are forced by circumstance to take the polygraph. In those situations, there are ways to foil the CQT based on the knowledge that it entails comparing your responses to the relevant and the "control" questions.
Finally, and most importantly, if the examiner says that the polygraph has found you "guilty" or "deceptive", then leave immediately rather than trying to defend yourself. You then avoid the "post-test" interview phase, which is really an interrogation in disguise. If you provide a confession during this phase, then, even if the polygraphic evidence itself is not admissible in court, the confession, prima facie, is, and can be more damaging to you than the polylgraphic evidence itself.
John J. Furedy, Ph.D.
Professor of Psychology, University of Toronto
Cross appointed at Center for Brain Research, Ege University, Turkey
Board Member and Past President, Society for Academic Freedom and Scholarship