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What is a polygraph?

The polygraph is a scientific instrument designed specifically to record various physiological changes that occur in the human body at the time case relevant questions are asked. The Examiner looks for those changes indicative of deception and forms an opinion about your truthfulness, based on certain specific criteria.

What does the Polygraph record?

Your polygraph test will be administered using a Computerized Polygraph system. During the polygraph test we will record various aspects related to activity in your upper body and its resultant effect on your breathing, changes of electrical conductance and resistance within your skin, (EDA), as well as multiple aspects of your cardio vascular activity, including your pulse rate. Various activity sensors will also be utilised to monitor you for occult body movements (e.g. shifting around/showing physical discomfort etc.).

How does a Polygraph work?

The Polygraph records physiological (biological) changes that occur in the human body. These changes are evaluated based upon changes that occur when specific questions are asked. Most of us can remember a time when we lied to our parents or another significant person. We could feel the changes in our bodies. Often we can feel our heart racing, palms sweating, and other symptoms of apprehension (being afraid of being caught out lying).


When we evaluate the polygraph charts, we can see up to 32 different physiological changes indicative of lying. Knowing that we are lying makes us feel completely different from just being nervous. Simply put, the process of lying is more complex than that of telling the truth and also always holds risk. The body’s functionality changes as a result of this increased activity and these changes can be measured; much in the same way as a change in core temperature can be measured using a thermometer.

How accurate are polygraph tests?

There have been more than 100 published scientific studies of the accuracy of polygraph testing. On average, the overall accuracy of a properly administered polygraph test has been found to be in the region of between 88% and 92%, depending on the format of testing used. 


The accuracy rate of the process is, however, dependent on many factors. Research on the various formats and research projects undertaken in this regard are available here.


Polygraph compares favourably to other forensic tools used, as can be seen in the table below. In clarity, we would like to add that the percentages indicate the ability of the listed methodologies to identify the perpetrator and are not reflective of the processes themselves.

Table - FAQ

It is vitally important to note, however, that the expertise of the polygraph examiner ultimately determines the success or failure of the entire process. If standards are not met and the correct protocols not followed, the entire polygraph examination will be irreversibly flawed. It must be remembered that, as is the case with all forensic evidentiary processes, polygraph is a tool and not a comprehensive solution to any investigative situation. Only engage appropriately skilled polygraph examiners who maintain international testing standards and who are able to explore the evidence gathered during such undertakings, as mere pass or fail results have little or no value in reducing risk within any given environment, without substantiating evidence or where questionable and/or sub-standard processes are evident.


All our polygraph examiners are internationally accredited and work to strict standards. They are all well qualified and have extensive investigative backgrounds. Resolution of failed test outcomes is our forte, with complete resolution of all tasks undertaken our main objective. Contact our head office in Cape Town on 021 555 1411 for more details.

How are these recordings made?

The recordings of your respiration (breathing) patterns, as well as other related activity are accomplished using two strain gauges, one across the chest and the other across the abdomen (stomach). The ability of your skin to conduct electricity is recorded by placing two electrodes on the fingers or using electrode pads on your palm. Cardio Vascular (heart) activity is recorded using a standard blood pressure cuff placed on the upper arm, forearm or calf.


All polygraph examinations must be audio-visually recorded for the safety of examinees, as well as for quality control purposes.

Will the test hurt?

The test is painless. There is no electricity, bright lights, bells or whistles. The only physical thing felt during the polygraph test is the pressure of the air against the skin in the blood pressure cuff. When your blood pressure is taken by a doctor, the cuff is inflated to approximately 200 mm hg. The Polygraph Examiner will inflate the cuff to approximately 70 mm hg. As the test progresses, the cuff may feel tight, however, the cuff is only inflated for three (3) to four (4) minutes. The fingers may tingle but the discomfort is brief/passing and easily managed by the examinee.

What if I am nervous?

The average person will be nervous during the administration of a polygraph test. In fact, a certain level of nervousness is expected by the Examiner. Although the increase in physiological activity will be recorded and clearly visible during chart collection, (increased heart rate, etc.) this will not affect the test itself, its accuracy or the scoring process. Simply put, you cannot fail a polygraph test due to nervousness. The mental effort taken to lie is much greater than that used to tell the truth (cognitive load) and this, together with associated changes in the nervous system relative to increased risk whilst lying, not nervousness, is effectively what is being measured.

Are there different types of “lie detectors”?

There are several types of polygraph instruments on the market today. Each instrument records the same basic psychophysiological data as described above. The older instruments generated recordings using ink and paper but modern day technology uses a computerised system. Polygraph testing should not be confused with those who claim to detect lying using “voice stress analysis.” It is important to know that every independent scientific research project assessing the “voice stress” technology to date has found the test to be accurate between 47% and 52% of the time, which is little more than chance (flipping a coin). As such, the scientific community does not recognize “voice stress” as a reliable way to detect truth or deception.

Are polygraph examinations and their results accepted in judicial forums?

In terms of the Law of Criminal Procedure and Evidence, the only test as to admissibility of any form of evidence into any given judicial forum, is relevance. Once admitted, it is up to the presiding officer to attach weight and value to such evidence.


As such, polygraph testing and the results of such tests, as well as the evidence gathered during such processes is acceptable and admitted into evidence at disciplinary hearings, the CCMA, labour court and in some circumstances, our criminal courts.


Of primary importance in all such instances is the ability of your examiner to have himself/herself declared both a specialist and reliable witness. This will require sound credentials and references as well as very detailed knowledge of the processes, procedures, ethics and application of polygraph testing. The ability to testify with authority and competence as to the evidence gathered by way of such interventions is crucial.


All True Lies Polygraph Examiners are trained to international standards and also undergo additional, advanced training on a regular basis to ensure that their skills are current, relevant and of course admissible in terms of the laws governing the collection and presentation of evidence gathered during our investigative processes. Care is also taken to regularly test all polygraph equipment utilized by our Examiners and equipment functionality certifications are renewed annually. Our Cape Town head office is available to advise you accordingly, should you require further information.

What will happen during the actual polygraph test?

When you first meet with the Examiner, he will be based in a fairly quiet room, where disturbance can be avoided. Your rights in terms of the test will be explained and you will be asked to sign a statement indicating your willingness to participate. The Examiner will then collect basic data about you, for the purpose of the test. General questions about health and for e.g. substance abuse may be asked. These questions help the Examiner to determine if any suitability problems exist that could have an adverse impact on the testing process.


The Examiner will comprehensively discuss the format of the test with you, certain aspects of your personal history which may have a bearing on the test, as well as the workings of the polygraph instrument. Once the preliminary questions have been asked and information obtained, you and the Examiner will discuss the matter under investigation. During this part of the test, you are given the opportunity to explain what you know about the matter under investigation. 


You and the Examiner will discuss the allegations (specific issue testing) or your background (pre-employment testing). After discussing the matter under investigation, you and the Examiner will discuss questions to be asked during the data collection phase. You will be informed of the exact wording of each and every question to be asked during the test. If you are not told what questions are going to be asked, you should not take the test.


If you are mistreated in any way or asked unusual or improper questions, report the incident immediately to the most senior member of management available on the day.


The entire polygraph process must be recorded on video camera. Should you need to rely on physical evidence to prove that the correct procedure had not been followed, this will be made available.

Are personal questions asked during a polygraph examination?

During the testing process, you may be asked personal questions that relate specifically to the matter under investigation. If you have concerns about the need to make a specific inquiry, ask the Examiner, who will explain the purpose of the inquiry. If you are not satisfied, you have the right to refuse to answer any question asked.

What outcomes can I expect from the polygraph test?

At the conclusion of the test, the Examiner will review and score the psychophysiological data, based on various criteria and the examination technique used. The opinion of truthfulness or deception is based solely on the aforementioned assessment. Finally, the Examiner may use a computer algorithm to analyse the data, which may either support or bring into question his/her initial finding. In certain cases, the data may be sent to an independent second Examiner for further analysis as an added process, prior to releasing final results, which are usually given to the examinee immediately after conclusion of the examination.

I take medication. Will this interfere with the test?

Taking medication prescribed by a physician or purchased “over the counter” will not usually interfere with the testing process. If you are taking medication, give the Examiner a list of the medications taken. Never discontinue taking medication without the specific approval of your medical doctor.

What about marijuana and other illegal drugs?

The use of illegal drugs is one of the most common chemical countermeasures used in polygraph testing. There are no legal or illegal drugs that will allow someone to “beat” the test, per say. Users of illegal drugs are detectable by irregular changes in normal physiological reactions, based on the effect these substances have on the human body. Most Examiners assume the use of chemicals to beat the test as an indicator of deception or guilt. It is important to remember that some illegal drugs increase the size and duration of reactions. If you are going to tell the Examiner the truth, you are better off avoiding prescription medication not prescribed to you or use of illegal drugs.

What about Internet sites describing “How to Beat the Polygraph”?

There are several sites on the Internet devoted to “beating” the polygraph. Without an extremely high level of professional training and on-going access to a polygraph instrument (such as available to certain government agents), the information and advice given on the aforementioned sites is of little value and in fact, often exposes a deceptive subject as being purposefully non-cooperative very quickly after the onset of his/her examination.


Simply put, the application of the “techniques to beat the test” is easily detectable and generally ineffective.


Anyone using any form of countermeasures is immediately classified as a viable suspect in the matter under investigation and is dealt with as effectively having failed his/her test.

Are criminal suspects or others “required” to take a polygraph test?

Polygraph testing is a voluntary procedure. You cannot be “forced” to take a polygraph test. However, under certain circumstances, adverse consequences may result if the test is not taken or if it is failed.

Who uses polygraph testing?

Today, polygraph testing is used by every major law enforcement agency in the world, including the South Africa Police Service, as well as various government departments. Prosecutors may use polygraph testing to assess a case before filing at court, particularly to verify the truthfulness of witnesses. Defence Attorneys may use testing to determine his/her defence strategy, especially in the USA.


Most employers in South Africa may include routine polygraph testing as both a pre-employment measure, as well as honesty control measure during employment. Where sensitive information, valuables and cash money are handled, routine polygraph screening forms part of the ongoing process of ensuring that integrity of the working environment is maintained. Bank employees, jewellery manufacturing, mine workers and drivers who move valuable cargoes such as cash or easily saleable goods are most often routinely tested.

Are polygraph tests and results confidential?

Prior to the polygraph test, you will be asked to sign an authorization to release the interview and test results. The person or persons to receive the test results will be disclosed to you. As a general rule, test results are confidential. Exceptions to confidentiality occur when the Examiner is a “mandatory reporter” involving child sexual or physical abuse and the test is not conducted for an attorney.

Can I dismiss an employee based on a failed polygraph result?

The short answer is a definite yes but, as in the presentation of all evidence, certain rules apply and the following needs to be considered: Polygraph testing, when correctly utilised, is primarily used to narrow the focus of any investigative process, not to replace it. Findings should always be corroborated. All forensic evidence, including such cases where latent fingerprints are found at a scene of crime for example, only have value when presented in conjunction with supporting evidence relative to the situation under investigation.


As such, you most certainly can use the polygraph and the evidence gathered during such processes to effect the dismissal of an offending member of staff, provided correct procedures are followed during the aforementioned polygraph examination and sufficient evidence exists to verify/corroborate any given failed outcome. For this reason we are very dismissive of mere pass or failed results, as often tendered by other examiners in the field, as this practice has limited application.


Our polygraph Examiners are focused on the resolution of failed outcomes and have the necessary skills to pursue these results. This ability is critical in so far as the application of such processes, in order to successfully manage risk in respect of any given undertaking. As such, we have assisted many clients with their internal investigations, polygraph requirements and the subsequent defence of their investigative processes in various judicial forums, as well as at the CCMA in Cape Town and nationally, as specialist witnesses.


A critical link in the chain of evidence and its admission, especially based on the administration of any given polygraph examination, will always be the credentials and ability of the Examiner, the manner in which he conducted the investigation, as well as his recordkeeping throughout. Professional standards in terms of such polygraph examinations, ethical practices, as well as the gathering of evidence in terms of the law of Criminal Procedure and Evidence, are all factors which must be considered during the course of every investigative undertaking.

What happens if a staff member refuses to undergo a polygraph examination?

Polygraph testing is a consensual process. Nobody can be forced to undertake an examination, under any circumstances.


This does not mean, however, that investigation of risk and/or any specific incident cannot proceed and that a mere refusal effectively shuts down the ability of any given party to pursue such matters. In short, standard investigative methods will have to be followed in order to proceed with any investigative requirement under such circumstances. We have developed very effective ways of dealing with such cases. For advice in this regard, please contact our head office in Cape Town on 021 555 1411.

Should I inform my staff members about the date on which they will be undergoing the proposed polygraph examination?

There is no legal obligation upon you to do so as no preparation for polygraph testing is required. To inform examinees of specific testing dates often results in absenteeism on that specific day. It is strongly advised, however, that you do receive signed documentation from your staff members indicating their willingness to participate in the proposed polygraph process, without disclosing specific dates on which this would commence.


A template of this document can be obtained from our office.