Is the Polygraph a Standard of Proof?

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The polygraph or lie detector test is used by many to determine if someone is telling the truth about certain questions asked. However, the truth about this device demonstrates how the processes used to ascertain what is considered the truth do not provide enough of a basis to constitute the actual truth of the questions.

The myth of the lie detector test is greater than what results provide to the investigator attempting to determine the truth of such questions. In the stories and in television, the polygraph proves conclusively that the person under inquiry is either telling the truth or lying about various statements asked. However, the truth behind this device is that the answers are analyzed through psychological and physiological responses to the questions. The person sweating or stammering may be an indication of deception. Additionally, many are able to pass due to elevated heart rate or inducing pain. This may not be enough to constitute the machine as a standard of proof, as the results are not admissible in court.

Lie detector tests pick up the physiological changes a person goes through when connected to the machine. However, some of these responses to the questions are nerves, emotions or stress. This then causes the testing to fail for certain questions, all questions to have incorrect responses or for the entire test to pass when the individual was lying. Additionally, there are some medical conditions that are read as an answer to a question when it is the body and not the person’s reply. Because of the known issues with these devices, the screenings are not considered admissible evidence even when they’ve been obtained for an investigation.

Polygraph Explained

The lie detector machine measures certain changes in the body. This may involve heartbeats, emotional stirrings that may indicate stress and similar physiological alterations. Through the paper and pen marking these changes as they occur, experts are expected to know exactly what these waving lines mean. However, sometimes they occur without any question asked. If the individual is stressed or anxious, this usually shows on the paper. When combining heart rate, blood pressure, breathing and skin conductivity with the machine, the experts are able to measure what this means in context to the questions and answers. And while the movies and television make this easy, the reality is far from a simple yes or no about the truth.

Even with the computers used in the electronic age, the results are not usually as clear as made out by movies. Some of the equipment is tight and uncomfortable on the body, and this triggers an equal response. Additionally, where the probes are placed could register skin triggers to cold, heat or emotional turmoil. Respiration scans may report an increase or decrease that is used to determine truth from lie, but the subject may experience nervous fits or similar states when confronted with a polygraph machine. If the questions are complicated or jarring, the individual may also experience higher rate of heart beat and breathing along with sweating.

Standards of Proof

When considering the factors of a case, the evidence used to demonstrate guilt or innocence of a person in criminal cases must be beyond reproach. While many experts and elements are included that are not without downsides, some factors are not involved because of the myriad problems that are discovered. Because of these factors and similar circumstances, the polygraph is not admissible in a court of law. The responses are not based on standard guidelines but someone interpreting the results. Additionally, the devices are unable to distinguish between false positives, lies and truths due to the problems of physiology.

Further standards of proof are provided by scientific processes that are reproducible by experts that have studied a field of practice for years or decades. The body is capable of exhibiting responses based on emotion, and emotion may help the individual lie. These issues throw off the true results, and this indicates that a lie detector does not always capture and record truth. This ends with the polygraph as something far from a standard of proof, and it should not be used until there are better detection methods available.

Legal Help with Polygraph

Law enforcement, the courts and legal representatives all may have enough knowledge about the polygraph to ensure that the results are inadmissible in court. However, some persons are subjected to the machine beforehand, and these results may affect the individual. A lawyer should be hired to ensure the rights of his or her client are protected.


Disclaimer: While every effort has been made to ensure the accuracy of this publication, it is not intended to provide legal advice as individual situations will differ and should be discussed with an expert and/or lawyer.

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