What is a Polygraph Test?
A polygraph test (commonly referred to as a lie detector test) is an instrument that measures and records several physiological responses, such as blood pressure, pulse, respiration, and skin conductivity. At the same time, the subject is asked and answers a series of questions because false answers will produce distinctive measurements.
Within the U.S. federal government, a polygraph examination is also known as a psychophysiological detection of deception (PDD) examination. Several other technologies are used in lie detection, but the polygraph is the most famous.
Polygraph Machines
Polygraph machines measure physiological changes linked to the sympathetic nervous system during questioning. However, their accuracy and reliability are widely debated. Physiological responses do not definitively indicate deception, as nervousness can affect results for truthful individuals, while some dishonest individuals may manipulate their emotions to pass the test.
Contrary to popular belief, polygraph tests are not commonly used in investigations, as their results are often inadmissible in court. Judges have discretion over accepting them as evidence, but courts are not obligated to do so.
Are Polygraph Results Admissible in Court?
The admissibility of polygraph results in court varies significantly by jurisdiction and circumstance. In general, polygraph results are not admissible as evidence in most courts across the United States and many other countries. This is primarily due to concerns about their reliability and accuracy.
Courts generally consider polygraph results to be unreliable for several reasons:
- Accuracy Concerns: Polygraphs can produce false positives (indicating deception when none exists) and false negatives (failing to detect deception when it is present). The accuracy of polygraph results is debated among experts, and they are not considered foolproof.
- Subjectivity: The interpretation of polygraph results can vary between examiners, making them subjective rather than purely objective evidence.
- Legal Precedent: Many courts have ruled that the potential prejudicial effect of admitting polygraph results outweighs their probative value, meaning they could unfairly influence a jury or judge.
- Rights Against Self-Incrimination: In some jurisdictions, admitting polygraph results may infringe upon a defendant’s rights against self-incrimination, as it could be seen as coercing them into submitting to a polygraph examination.
Despite these general trends, there are exceptions. Some jurisdictions may allow polygraph results under certain conditions, such as when both parties agree to their admissibility or when they are used for limited purposes, such as plea negotiations. Additionally, some administrative or non-criminal contexts may accept polygraph results more readily, such as in some employment screenings.
Polygraph Test Resources
The following are resources for polygraphs, testing, and related resources.
- American Polygraph Association—The largest organization for truth verification specialists worldwide. It represents the interests of examiners in government, law enforcement, and private business and provides access to helpful resources, publications, and training.
- Federation of American Scientists: Polygraph Policy – An extensive list of official documents, articles, and other resources on polygraph testing.
- How to Pass a Polygraph Test – Prepare to pass the test by knowing how to produce a truthful chart consistently. Almost half of the time, you’ll be branded as a liar if you’re nervous when you take the test. The tests are often inadmissible because they are not true lie detection.
- National Polygraph Association—The Organization aims to promote and advance public acceptance of the polygraph and urges members’ active participation in civic and community affairs. It includes helpful resource links and tools and allows you to search for a certified examiner. It also provides membership for existing examiners.
- Polygraph Evidence in Court – Examining lie detection results as a sensible approach to the problem of wrongful convictions due to perjury by police, jailhouse informants, and cooperating prosecution witnesses. Although it is a helpful website, it contains a lot text, long pages, and links. It may take a while to sift through and find what you need.
Hire a Private Investigator to Help
Some private investigators offer polygraph examination services. Visit our Private Investigator Directory to find a polygraph examination provider in your area. Also, see our article on DNA Lab Testing and Analysis.
Questions and Comments
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