A polygraph is a three part test that measures various physiological processes that can indicate whether a person is telling the truth about an event, experience, or past action.
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 investigators 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."
Polygraph testing isn’t just for criminal investigations. There are many situations in which you can ask or be asked to take a polygraph test.
The examination is administered by a trained investigator and can take up to two or three hours, possibly more depending on the scenario. It is comprised of three parts:
The pre-test is a conversational interview during which the examiner makes a judgement as to whether the person is capable of being polygraphed. The examiner will ask questions involving the person’s amount of sleep, medication use, drug use, and 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."
During the test portion, a physiological recorder measures three bodily indicators that reveal when a person lies:
Heart Rate/Blood Pressure
Cardiovascular activity is measured by a blood pressure cuff.
Breathing patterns are captured by pneumographs wrapped around the subject’s chest.
Perspiration is documented via electrodes attached to the fingertips.
While the polygraph measures reactions, the examiner will ask a series of questions. Sometimes, the same question will be asked multiple times in the search for consistent significant reaction or lack thereof. The questions include control questions that set a base for relevant questions, which are directly related to the reasons for taking the polygraph. In theory, a truthful person will react more significantly to the control questions than the relevant questions.
Note: A polygraph measures what a person believes to be the truth, not necessarily what actually happened.
Image source: Wikipedia
Once the test is complete, examiners measure the reactions and come to one of three possible 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.
The accuracy of polygraph testing is a highly debated subject mostly because human reactions are not standardized. An honest person may act nervous while a deceptive person might maintain calm. There’s also little research that examines whether outside factors, like education or intelligence level, affect the test.
However, in 2002 the National Academy of Sciences conducted a comprehensive review that concluded polygraph testing to be better than chance even if it fell short of complete accuracy. Raymond Nelson, president of the American Polygraph Association, claims the accuracy rating is above 80%.
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