How do polygraph tests work, and how accurate are they?
What is often referred to as the polygraph” is actually a set of relatively complex procedures for asking questions and measuring physiological responses in order to detect deception or establish truth. Polygraph testing is employed for a variety of uses, ranging from ascertaining the guilt of a criminal suspect to assessing the honesty of a prospective employee. Because different polygraph procedures are required depending on intended use, it is necessary to consider validity by polygraph technique and situation. The courts have found themselves disagreeing on methods to establish validity for purposes of admissibility of evidence, where the critical focus of such judgment should rest. In addition, courts are inconsistent about what decision to make on the basis of judicial findings of fact regarding the validity of a diagnostic or predictive device. So, in summary there is really no agreement as to the accuracy of polygraph testing. People have been known to “beat” the machine and al
Most people are uncomfortable lying. Lying tends to produce a slight increase in one’s stress levels. A polygraph attempts to detect these changes in stress levels. The whole process is highly subjective, of course. If the subject is being asked questions which he is not comfortable answering, he may actually experience more stress giving a truthful answer than telling a lie. It seems clear to me that a polygraph can be expected to produce results of very limited accuracy. The skill of the person using a polygraph plays a big role in it. Many years ago, someone close to me had a very bad experience with a polygraph examination. Some money appeared to have gone missing from the place where this person worked, so all the employees were made to take a polygraph test. This person failed the test, and was declared by the polygraph operator to be “as guilty as hell”. This person, of course, was fired from that job. It later turned out that there was no money missing; only a minor bookkeeping
A co-worker of mine took a polygraph test and one of the questions that came up was whether you have stolen- A.) More than $1000 B.) Between $300 and $1000 or C.) Less than $300. She chose letter C. And they determined that she was lying about it but when she was later confronted with the question she said that she chose letter C because she had not ever stolen anything in her life. So technically she “lied” but it was over a question that would not give her the opportunity to tell the truth. And that is one of the problems with accuracy- Not every examiner will ask the right questions or do a post test interview in order to make an assessment of whether or not this person is lying. As humans we are not perfect as it is. Certainly we ought not depend on a machine to tell us who we should trust. A former federal agent once told me that a polygraph machine is nothing more than an intimidation tool that they use to get a confession out of a suspect. What they would do many years ago is sh
They measure a number of different physical symptoms at the same time (which is why they are called polygraphs). Particularly heart rate, breathing rate, blood pressure, and skin conductivity (i.e. sweatiness). The idea is that if you know that you are telling an untruth, you may be able to keep all all conscious symptoms, like your face and voice, under control, but you cannot affect these involuntary symptoms. If several of them jump together (a matter for interpretation by the operator) you are probably lying. I do not believe that they work except with a very skilled operator and under a level of intensity of questioning which would amount to interrogation, not questioning. And I certainly don’t believe that the results would be appropriate for court or employment use. At best they can be a straw in the wind telling you that there is something to look for. Answer originally posted in response to How do ‘lie detectors’ work?
