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The truth about polygraph tests AKA lie detectors

10September, 2019

The accuracy of polygraph tests has been disputed since the day they were invented. We often see them in popular culture, crime dramas and reality television, but how do they really work? Can they go wrong, and what do the results really mean? 

Often used in infidelity investigation, polygraph testing is still a popular method and definitely something to consider if you are conducting your own private investigation.

How it works

The instrument used in polygraph tests is there to assess three indicators – heart-rate/blood pressure, breathing and skin conductivity (by the electrodes you often see attached to the ends of the subject’s fingers).

Before they start the test, they will explain the technique and ask some test questions – this is to induce some concern in the subject about being deceptive.

The subject is then asked a series of questions designed to find out if they are lying.

If the instrument detects a large physiological reaction to a question, especially in comparison to other questions, then this leads to the diagnosis of deception.

What causes inaccurate results?

There is no evidence that there is a certain pattern of physiological reactions that are unique to telling lies. It is believed that nervousness and anxiety may lead to inaccurate results. 

There has been some research into so-called countermeasures, strategies that claim to be able to “beat” polygraph tests – but to beat a polygraph test, the subject would need strict training and most examiners will spot attempts to cheat.

What do the results really mean?

They’re not a perfect science, but polygraph tests have been proven to offer key insights into whether someone is telling the truth. There have been many studies that validate polygraph tests for detecting deception. A well-trained examiner can usually confidently say whether someone is telling the truth, whether their results are impacted by nervousness, or whether they are telling an outright lie.