Lie Detector Test – Can It Be Used as Evidence?

Lie Detector Test – Can It Be Used as Evidence?

While the use of a lie detector test (via a polygraph machine) as a tool for detecting if someone is lying is regularly used on American TV shows, there is the question of its use to provide admissible evidence under Australian law.

How does a lie detector test work?

There are two basic types of polygraph:

  1. One detects variations in the level of stress and vibration in a person’s voice under question; and
  2. The other measures the physiological reactions of the person under question. The types of physiological reactions measured are changes in pulse rate, blood pressure or any muscular activity and these are then interpreted against some baseline (known response) answers.

Is evidence from a polygraph admissible in Court?

A number of Australian legal cases have considered the admissibility of evidence derived from a polygraph machine and as a general rule have determined that it is not admissible. There are a number of reasons Australia courts don’t accept evidence from a polygraph machine, such as:

  • The polygraph operator although interpreting the questioning of a possible witness, is only expressing their opinion of the facts of the issue.
  • The jury should be able to determine the facts, presented by the witness who perceived them by their physical senses not an operator interpreting a witness’ statement.
  • The polygraph operator is just an operator, not a qualified expert witness.
  • The scientific basis of the polygraph is questionable, so evidence provided by a polygraph operator is considered hearsay.

For the many people who claim that the polygraph is fail proof, there are an equal number of people who claim that a polygraph can be beaten. For this reason, until the science is proven it is unlikely that current forms of lie detection will be admissible to an Australian Court.

That said lie detection test services are available throughout Australia and the inadmissibility in court hasn’t stopped the police and parole boards from considering evidence collected in the course of their investigations.

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