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
The polygraph machine measures physiological changes caused by the sympathetic nervous system during questioning.
Many people wonder if lie detector tests are accurate and reliable. There is no proof that certain physiological reactions mean a person is lying or deceptive. For example, an honest person may be nervous during a test, affecting the results. In contrast, a dishonest person may know how to control their emotions and beat the test.
Another common myth is that polygraph testing is used in every investigation. The tests are rarely used because the results aren’t always admissible in court. Courts are not required to allow lie detector test results as evidence. Individual judges have the authority to decide whether the results can be used.
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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