A polygraph is a test that measures whether a person is being truthful about an event, experience, or past action through monitoring of various physiological processes. The examination is administered by an investigator and can take up to two or three hours, possibly more depending on the scenario. The test is comprised of three parts:
The Pre-Test is a conversational interview during which the examiner makes a judgment as to whether the person is capable of being polygraphed. The examiner will ask a series of simple questions, like how much sleep the person has had, what medications they are on, and what they've read about the test, to help determine that the person’s mindset is not muddied by drugs, alcohol, or mental psychopathy.
"I need them to have a grasp of reality at the time of the event and in the polygraph exam room," expert polygraph examiner Jack Trimarco says. "It's an evaluation to be sure that this person can receive a polygraph test that is going to be valid."
Once the Test portion has begun, the questions are asked two, three, and sometimes four times in a particular format. During the exam, the examiner is looking for consistent significant reaction or lack thereof.
What is consistent significant reaction? The reaction is how the body changes when a person decides to tell a lie. The physiology begins to change. Breathing changes in a predictable way, the sweat glands activity innervates, and the person’s blood pressure goes up. This reaction takes place for three to five seconds until everything goes back to normal. Consistent significant reaction means that the same reaction is present multiple times, which is why the questions are asked more than once. Each time a question is asked, a decision is made numerically.
Note: A polygraph measures what a person believes to be the truth, not necessarily what actually happened.
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Once the Test portion is complete and numerical decisions are made the charts are scored and the examiner comes to a conclusion. There are three potential conclusions:
No opinion, formerly referred to as inconclusive, means that the investigator could not determine whether or not the person was telling the truth. About 10% of lie detector tests result in no opinion.
There are ways to mess with the test, but they're all observable. If a person tries to alter the test, they generally get a warning from the examiner. If the person continues, the test stops and is deceptive by virtue of countermeasures. Countermeasures are methods the investigator uses to detect when the person is trying to alter the results of the lie detector.
Trimarco notes, "It's very, very difficult for a person with no polygraph background to sit down and mislead a former federal examiner or someone who has an education in countermeasures."
Polygraphs are used in a variety of scenarios. In personal matters, one person may ask another to submit to a lie detector test to ensure that they are being honest and truthful, be it a potential nanny, a spouse, or some other individual. These tests are also used in hiring, often for federal or high-level security positions, and in some legal matters, depending on the court and case.
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