Polygraph tests can’t tell when you are lying

THE EDITOR: Some police officers have been transferred by the Commissioner of Police for refusing polygraph tests. The cops have blanked the lie detector tests. No lie.

The question of whether polygraphs are a good way to figure out whether someone is lying was settled long ago. They are not.

There is no unique physiological sign of deception. People watch you in your eyes and lie all the time. Tell me I lie.

There is no evidence whatsoever that the things the polygraph measures – heart rate, blood pressure, sweating and breathing – are linked to whether you are telling the truth or not.

Research in scientific psychology and physiology provides little basis for the expectation that a polygraph test could have extremely high accuracy.

There is simply no consensus that polygraph evidence is reliable. And yet polygraphs are still routinely used by government agencies and law enforcement. Why should we rely on pseudoscience to solve crime, Mr Commissioner?

There was never any complete theory of the physiology of the lie. The three measures – blood pressure, respiration and sweating – are all different physiological systems. A polygraph measures one thing – anxiety. The more practised you are at lying the less anxiety is associated with it.

A polygraph test can sometimes be correct and sometimes be wrong. When accused of an actual crime, many people become anxious even if they are innocent.

A polygraph is used as a prop, a part of the theatre of interrogation minus the ice, wet towel and drawer. The subject is tricked into believing his lies can be detected and he confesses.

A polygraph can be seen as a deterrent if an offender believes he is going to be subjected to tests. The test is perceived as effective. Perceived.

We in TT want to believe in a just land where no one can escape lying. Any human designed test can be beaten.

AV RAMPERSAD, Princes Town

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