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Frequently Asked Questions

How reliable is the Polygraph?

To answer this question we always quote the answer as answered explained by Clifton Coetzee in his book Truth Extraction Contd – How to Analyse Eyes & Lies –

“How reliable is the polygraph? Well, that depends on whom you ask, but I say that the technique is accurate but not infallible. Mistakes do occur and the examiners usually cause them – either because they failed to properly prepare the subject for the interview, or by a subsequent misreading of the polygraph charts.

These errors are often referred to as ‘false positives’ or ‘false negatives’. When a truthful subject is reported as being deceptive then a false positive is the outcome, while a false negative is just the opposite – an untruthful subject is reported as being truthful. Either way, the examiner takes the situation very seriously and they often go to great lengths to overcome the problem and protect the credibility of the system.

The examiner will often go through the test with the subject afterwards to offer them the opportunity to explain unexpected physiological responses. They will also take into account a variety of other factors, including the subject’s emotional state at the time of the test and any medical information they have about the subject’s physical condition. They’ll run tests to determine if the subject is overly nervous or under the influence of tranquillising drugs. They will look particularly at comparison questions asked during the course of the examination. These are designed to evaluate the subject’s response capabilities.”

  • © Clifton Coetzee 2013 Published and printed in South Africa 2013 ISBN 978-0-620-52413-1 –


Is There Any Law Controlling Use of Polygraph in South Africa

  • Currently in South Africa there is no Legislation at this point to control the use of the test or to protect the employee’s right against the abuse of the test, however Polygraph testing are accepted in our Common Law as corroborating the burden, and therefore add to the quantity of proof, therefore bringing it closer to the actual truth.


 Can one be Compelled to Undergo a Polygraph Test?

It is against the Constitution of South Africa to compel a person to undergo a polygraph examination, unless she or he consents to it. The consent must be in writing.

  • The individual should be informed that
  • the examinations are voluntary;
  • only questions discussed prior to the examination will be used;
  • he/she has a right to have an interpreter, if necessary;
  • should he/she prefer, another person may be present during the examination,
  • provided that person does not interfere in any way with the proceedings;