Polygraph Testing

Polygraph Testing

The truth about polygraph testing


How can an instrument tell a truth from a lie? This is the controversial question people have been asking since the invention of polygraph testing. In the same breath, many ask how it is possible that we all have the same physiological reaction when telling a fib. We will get to that, but despite the doubt surrounding the service, there is a reason polygraph testing has stood the test of time and is a household term all around the world. In just a few minutes of reading, find out the most important things you need to know about polygraph testing and our company, Polygraph Truths, who provides you with this reliable service.

What is polygraph testing?

Commonly referred to as a lie detector test, the polygraph is a procedure or device which serves to measure and record certain physiological indicators given off by a person when asked a set of questions. Stemming from the Greek term “polygraphos” which means “writing much,” the polygraph remains one of the most well-used interrogation tools known to date. While most polygraph examiners tend to use their own tried-and-tested scoring methods when conducting tests, the use of polygraphs is underpinned by the belief that deceitful answers will lead to the production of certain physiological responses and indicators in the subject that can be differentiated from the same responses that are associated with honest answers.

The main physiological indicators examined are; blood pressure, respiration, pulse and skin conductivity – and they can be described as the four horsemen of lie detection when it comes to the polygraph. In many countries, polygraph tests are used as respected interrogation tools for candidates for sensitive employment opportunities or criminal suspects. Oftentimes, companies make it a requirement for potential employees or candidates to sit through a polygraph test as part of the interview process.

The anatomy of a polygraph instrument used for polygraph testing

As previously mentioned, the purpose of a polygraph instrument is to pick up a certain level of fluctuation in specific physiological processes and activities. Therefore it makes sense that the polygraph’s anatomy comprises the following:

Two rubber tubes filled with air which are placed around the subject’s abdomen and chest (known as pneumographs). When the subject breathes, the abdominal or chest muscles naturally expand and consequently, the air inside the tubes becomes displaced.

The pneumographs use transducers to convert the displaced air in the tubes into electronic signals to be read off a computer screen.

Next up we have the tools used to measure skin conductivity, or more scientifically, galvanic skin resistance. This essentially refers to the measure of sweat on your fingertips. Many people are unaware that the fingertips are a likely candidate for the most porous areas on our bodies – which is why monitoring sweat levels there is effective. This follows the notion that when placed under stress, we sweat more. The tools used for this part of the polygraph are known as galvanometres, which are fingerplates that are attached to two fingers. The plates serve to measure the ability of the covered skin to conduct electricity. When the skin is hydrated with sweat, electricity is conducted much more easily.


A blood-pressure cuff is secured around the subject’s arm to measure blood pressure and the heart rate. There is tubing that runs from the instrument to the cuff. As blood is pumped through the arm, a sound is made, which results in a change of pressure. This change in pressure displaces the air in the tubes and these results are converted into electrical signals to be read from a computer screen.

Polygraphs also often record leg and arm movements. As the examiner poses a set of questions, your bodily movements will also sometimes be noted and recorded.

Despite their mechanical nature, a large part of the polygraph test involves the individual observations of the examiner. These examiners are experienced professionals who have made use of tried-and-tested methods that go hand in hand with the polygraph instrument process, in order to give the most accurate results possible. There are unique signposts and indications of deception in human beings that can only be picked up with a knowing eye, which is why the human element of polygraph test and the examiner, comes in handy.

The abovementioned tools used in a polygraph examination would be useless if not accompanied with the right questions and methods that make lie detection instruments so effective. An examination includes a pre-test phase, a phase wherein the method is explained to the subject and each upcoming question is reviewed. This part of the process ensures that those sitting through the test understand the questions properly. However, it also serves to induce levels of concern about being deceptive.

The history of polygraph testing

Well before the invention of the first modern polygraph, scientists across the ages had been attempting to link vital signs with emotions. All the way back in 1858, a French physiologist by the name of Étienne-Jules Marey began recording the body’s responses to uncomfortable “stressors” such as sharp noises and nausea. Later, Cesare Lombroso – an Italian criminologist – took up the use of a specialized glove that measured a suspects’ blood pressure during interrogation. It was in 1921 that the first “original lie detector device” was built, however.

A Canadian psychologist by the name of John A. Larson was responsible for this particular invention. At the time he was employed by the Californian Police Service. His instrument, which he dubbed the polygraph, provided continuous blood pressure readings and recorded them on a drum of rotating paper. Near the beginnings of World War I, a Harvard psychologist known as Hugo Münsterberg reportedly used several instruments, one being a similar model to Larson’s polygraph, to both analyse and record subjective feelings – and he argued that the use of the instrument in criminal law would be beneficial.


It was only in 1939 that the first prototype of the “modern” polygraph was patented. Leonarde Keeler was responsible, and dubbed his instrument the Keeler Polygraph. Today, Keeler is still considered the “father of the polygraph.” His instrument recorded and documented the respiratory, heart rate and blood pressure of the individual undergoing an interrogation. His version was used successfully in various criminal investigations.

In 1993, it is said that the “computer age of the polygraph” first began. It was this year that the statisticians of John Hopkins University in the Applied Physics Laboratory created a software known as PolyScore. The software used an advanced mathematical algorithm to make sense of polygraph data and essentially establish the probability of a subject’s deceit or sincerity.

Legalities surrounding polygraph testing

In South Africa, the use of polygraph testing is a relatively accepted concept – and is particularly prevalent when it comes to labour disputes. However, despite this, there remains no official employment or labour legislation that controls or manages the test, nor any laws that protect employees from a potentially abuse of power at the hands of an unfair employer. For this reason, it is extremely important to treat anyone who you wish to subject to a test with respect and give them the freedom of choice when it comes to polygraph testing. It is mentioned in the South African Constitution that no one can be compelled to undergo a lie detection test without prior consent.

This consent must be in the form of writing, and is often included in an employment contract as a precautionary measure. There are specific instances where an employer his permitted to use polygraph test on an employee (if agreed upon in a contract):

  • To investigate questionable incidents
  • When employees have access to property of the employer that is the centre of an investigation
  • There is a reasonable amount of suspicion that said employee has been involved in misconduct
  • The employer has been subject to injury or economic loss and it is suspected to be at the hands of the employee in question
  • There is an ongoing investigation regarding contraband, abuse of narcotics, alcohol abuse or fraudulent activities within the business – and there is a reasonable suspicion that the employee in question has knowledge of it.

The relationship between polygraph testing and the CCMA

The Commission for Conciliation, Mediation and Arbitration is an independent authority that promotes fair work practices and procedures within South Africa. It serves to solve labour disputes as well as offer training and counsel where needed. You may have heard of this body before through a disgruntled individual explaining how they are going to go to the CCMA to question their dismissal or similar work problem. When it comes to polygraph testing and the CCMA, the authority has allowed examiners to stand as expert witnesses in cases wherein evidence must be tested for reliability. The CCMA Commissioner is then responsible for establishing whether or not their findings are admissible.


While polygraph results cannot be interpreted as guilt without reasonable supporting evidence, they are certainly regarded as a piece of useful information where other evidence of misconduct accompanies them. If an employer submits only a polygraph test result that serves as the sole basis for a dismissal, there is likely to be trouble. One test is not enough to take action against employees. However, as previously mentioned, the jurisprudence of South Africa does use the tests as corroborating evidence – which is showcased in the recent Mustek v Joseph Tsabadi NO & Others case in 2013.

If you are an employer feeling at a loss about whether or not to request an employee to undergo a polygraph test, you must first be sure of all the facts. This is to say that before you make any moves to organise a test, you must have given all concerned individuals the opportunity to come forward and explain themselves in the case of an incident. It is also important to know as many details of an incident as possible in order to give the examiner a good range of relevant questions to utilise in the test.

Polygraph testing offered by Polygraph Truths LS

We at Polygraph Truths LS aim to assist you in easing your troubles whether they be personal or professional. No one enjoys being lied to, especially when there is a lot on the line, which is why our experienced polygraph professionals as well as world-class polygraph instruments are available to set your mind at ease or alternatively – equip you to take decisive actions.