Psychophysiological Detection of Deception (PDD)

Frequently Asked Questions.

What is a Polygraph?

  • It is a test used to verify a person's truthfulness and is often called a 'Lie Detector Test.'
  • The word "polygraph" originates from the Greek word polugraphos (writing copiously), and means "many writings” or “many graphs."
  • The word “polygraph” eludes to the method used to continuously and simultaneously record specific physiological responses during an examination.
  • A Forensic Psychophysiologist (Polygraph Examiner) will utilize a computerized instrument to collect physiological data from at least three systems in the body. The Polygraph measures multiple physiological reactions, setting it apart from other less reliable methods. 
  • It is important to note that a polygraph does not include the analysis of physiology associated with the voice or micro muscle-tremor.
  • Instruments that claim to record voice stress are not polygraphs. (See section on Voice Stress).

How accurate is a Polygraph?

  • According to the American Polygraph Association over 250 studies have been conducted on the accuracy of polygraph testing during the past 25 years. Recent research reveals that the accuracy of the new computerized polygraph system is close to 98%.

From the American Polygraph Association:

“One of the problems in discussing accuracy figures and the differences between the statistics quoted by proponents and opponents of the polygraph technique is the way that the figures are calculated. At the risk of over simplification, critics, who often don't understand polygraph testing, classify inconclusive test results as errors. In the real life setting an inconclusive result simply means that the examiner is unable to render a definite diagnosis. In such cases a second examination is usually conducted at a later date. To illustrate how the inclusion of inconclusive test results can distort accuracy figures, consider the following example: If 10 polygraph examinations are administered and the examiner is correct in 7 decisions, wrong in 1 and has 2 inconclusive test results, we calculate the accuracy rate as 87.5% (8 definitive results, 7 of which were correct.) Critics of the polygraph technique would calculate the accuracy rate in this example as 70%, (10 examinations with 7 correct decisions.) Since those who use polygraph testing do not consider inconclusive test results as negative, and do not hold them against the examinee, to consider them as errors is clearly misleading and certainly skews the figures.”

Can Polygraph be used in the CCMA?

Polygraphists have been accepted as expert witnesses whose evidence needs to be tested for reliability. The duty of the commissioner is to determine the admissibility and reliability of the evidence. Polygraph test may not be interpreted as implying guilt but may be regarded as an aggravating factor especially where there is other evidence of misconduct. In other words, polygraph test results, on their own, are not a basis for a finding of guilt. It can be used only in support of other evidence.

Provided by the Commission for Conciliation, Mediation and Arbitration (CCMA)

Is there a law controlling the use of polygraph in South Africa?

Polygraph testing is a fairly new concept in South Africa, especially in disputes relating to employment relationships. There is no legislation at this point to control the use of the test or to protect the employee's rights against the abuse of the test.”


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;

When is the employer permitted to use a polygraph?

  • Generally, employers are permitted to use the polygraph to investigate specific incidents where—
  • Employees had access to the property which is the subject of the investigation;
  • There is a reasonable suspicion that the employee was involved in the incident;
  • There has been economic loss or injury to the employer's business like theft of company property;
  • The employer is combating dishonesty in positions of trust;
  • The employer is combating serious alcohol, illegal drugs or narcotics abuse and fraudulent behaviour within the company;
  • The employer is combating deliberate falsification of documents and lies regarding true identity of the people involved.



Who get the polygraph results?

  • Polygraph results cannot be released to any person but to an authorised person. Generally it is the person who has undergone the polygraph test (examinee), or anyone specifically designated in writing by the examinee, firm, corporation or government agency that requested the examination.

What are the protective procedures?

  • An assessment of the examinee's emotional state.
  • Medical information about the examinee's physical condition.
  • Technical questions to evaluation the examinee's response capabilities.
  • Factual analysis of the case information.
  • A pre-test interview and detailed review of the questions.
  • Quality control reviews.

Refusal to undergo test – Breakdown of the employer – employee trust relationship.

In Harmse & Rainbow Farms (Pty) Ltd.

In this matter the employee was one of 15 who had access or potential access to the missing equipment. When offered an exculpatory polygraph examination, Mr Harmse at first declined then changed his mind and did complete the test which he was the only person to fail. When offered another examination which could have led to his total pardon, he declined the opportunity and was then dismissed for reasons of breach of trust. The employer then dismissed him on the basis of not theft, but breach of trust relationship. This position and decision of the employer were upheld by the CCMA. Furthermore it was noted that:

“the employer has the right to dismiss an employee whom it can no longer trust provided there are reasonable grounds for such loss of trust based on the actions of the employee.
the employer had reason to request polygraph examination as a result of suffering a substantial financial loss.
an employer has a right in circumstances of such loss to exert some pressure on employees to cooperate in the investigation of the misconduct or crime.
granting of the option of a re-examination may be seen as a show of good faith by the employer.
the polygraph examination phase was seen as an integral and crucial part of the investigation.
the advance notification in writing of the examinees of the intention of the employer to institute polygraph examination as part of the investigation was seen to be fair.
the procedure was not viewed as an unfair labour practice nor as an infringement of the fundamental rights of the examinee.
the procedure underscored the fact that the examination was considered as voluntary.”

Prohibitive Inquiries:

Intrusive questions of a personal nature are not permitted in a polygraph examination. The American Polygraph Association, have so stated in language similar to the following:


  • religious beliefs or affiliations (unless specifically relevant to the job)
  • beliefs or opinions regarding racial matters (except to the extent that any such biases could interfere with one’s ability to fairly and objectively perform his or her job)
  • political beliefs or affiliations
  • beliefs, affiliations or lawful activities regarding unions or labour organizations
  • lawful sexual preferences or activities

Can an employee be dismissed for failing his/her Polygraph test?

No.  The Polygraph is utilized as an investigative tool used to direct investigations.  A polygraph on its own can never be conclusive proof of the guilt of an examinee.
“The results of the polygraph test cannot, on their own be conclusive of the finding of guilt, there must be evidence, other than polygraph results to support such a finding”

In Amalgamated Pharmaceuticals Ltd v Grobler NO and others (2004) 13 LC 1.11.3 The court found that it most definitely does not prove that someone is guilty. It is merely an indication of deception. The sole reliance by the employer on unspecific polygraph results is insufficient to discharge the onus in terms of section 192 of the Labour Relations Act 66 of 1995, to prove that the dismissal was fair. To discharge this onus, the test of a balance of probabilities is used. To only present polygraph evidence is not enough to show that the dismissal was fair because there is no corroborating evidence.

According to the well-respected Edward Nathan and Friedland Inc Attorneys in Sandton, the case of Mncube & Cash Paymaster Services (Pty) Ltd KN1583, 6 May 1997 showed that the Commissioner accepted the Polygraphists as an expert witness whose evidence needed to be tested for reliability.

In Hotellica Trade Union & San Angelo Spur WE3799, 24 November 1997, it was held that the lie detector test may not be interpreted as implying guilt but may be regarded as an aggravating factor especially where there is other evidence of misconduct.

Can someone undergo a polygraph examination to prove they are not lying?

It unfortunately happens that individuals are maliciously implicated in crimes or other false accusations and often have no recourse to prove their innocence or restore their honour and trust.  
The polygraph presents itself as a useful tool to restore the employer - employee trust relationship or repair the damage done by careless accusations.