What Does It Mean When Someone “Fails” a Polygraph?

Polygraph Test

A polygraph exam is not just a pass/fail issue. This is not a school exam where you are expecting to score something like 70% or above.

As Tiffanie Wen explained to the BBC , “polygraphs work by measuring physiological changes in the body, in this case respiration rate, pulse, blood pressure and galvanic skin response, which measures the electrical properties in the skin.”

Polygraph exams do not test intelligence or book learning. The test records a person’s autonomic nervous system (ANS) responses while a series of questions are asked.

Deception is indicated where the ANS displays a significant and repetitive “defensive” reaction to the relevant test question. If the lie detector expert administering the exam concludes that the ANS response to one of more of the questions indicates deception, the test subject is said to have “failed” the exam.

However, it’s important to understand that the deception indicated is not in itself a “lie.” But, repeated research and testing have found that 90-95 percent of people who have this reaction were lying in response to the question asked or withholding pertinent information relating to the question.

The American Psychological Association says, “Polygraph testing continues to be used in non-judicial settings, often to screen personnel, but sometimes to try to assess the veracity of suspects and witnesses and to monitor criminal offenders on probation. Polygraph tests are also sometimes used by individuals seeking to convince others of their innocence and, in a narrow range of circumstances, by private agencies and corporations.”


A lie detector expert may conclude that “the test subject cannot be excluded as a suspect” when those deceptive reactions are present. At the same time, it is important to note that some persons will “fail” a polygraph even though they are telling the literal truth but continue to hold back pertinent or incriminating information from the examiner.


Lie detector exam experts make conclusions based on the results indicated. They strongly suggest that no one make a life-altering decision based solely on the results of a “failed” polygraph test without the existence of additional evidence supporting this test result. – –