POLYGRAPH TESTING :
Article Date: 21 March 2002
POLYGRAPH TESTING - IS IT AS RELIABLE AND ACCURATE AS EVERYONE THINKS?
by Kerry Knowles
“Polygraph” as a term literally means “many writings”. The term refers to a device that simultaneously measures
and records selected physiological activities or electro-physiological activity. The device captures the minimum of
three types of psychological data, usually differential blood pressure, heart rate, respiration rate, and skin
conductance (subcutaneous sweating). In essence, this means that the person being examined will fear being
caught lying and his body will react reflecting that fear, which reactions are captured by the polygraph test. This
type of testing has been in existence for approximately 2000 years and not much has changed in the
technological aspect, except for how the data is captured or recorded.
WHERE THE PROBLEM LIES
The psychological measurements of the test are accurate. The problem lies with the inference that deception can
be determined from changes in this physiological activity. To date, there is no known device, which measures
physiological or psychological activity capable of directly recording deception. This is the criticism raised by Colin
Tredoux and Susan Pooley, who have written a paper (Polygraph Based Testing of Deception and Truthfulness:
And Evaluation And Commentary (2001): 22 ILJ 819) challenging the theory and method underlying the way
inferences are made from the polygraph’s findings on the physiological recordings. Simply put, the theory is
based on the assumption that physiological activity increases when a person is lying and the polygraph is used in
detecting that deception. There are generally two types of methods or tests used, namely the Relevant- Irrelevant
Test (RIT) and the Control Question Test (CQT). The RIT test is the oldest test, but has been widely criticised
over the recent past and is regarded a very weak form of control. In this test critical questions are relevant to the
purpose of the assessment, whilst the control questions are irrelevant. One would be held to be deceptive if the
physiological activity was greater in regards to the relevant / critical questions as opposed to the irrelevant /
control questions. The CQT test is presently more widely used and accepted. Here the test compares the
physiological arousal of the person in response to critical questions, in comparison to the level of arousal when
telling an unrelated lie. The latter serves as a benchmark against which the responses to critical questions are
measured. Basically, if the person’s response to a critical question is greater than that when answering the
control question, he is assumed to be deceptive. The converse is also true. This test has also been severely
criticised for a number of reasons, for example, ethically the person must be intentionally misled for the test to be
successfully conducted and methodologically, the confusion between the role of operator of the machine,
interrogator and as polygraph examiner. From a scientific point of view the control questions are not effective or
true control questions, as they would have to demonstrate that any increase in the physiological activity would be
solely attributable to attempts of deception, which is not possible as there may be any several other viable
explanations for an increase in that activity.
Therefore the theoretical rationale of polygraph testing being able to measure deception is questionable, as the
methodology used in conducting these tests do not measure up to certain scientific requirements, several
improbable assumptions form the basis of the tests and true forms of control are not used which makes it
unrealistic to rely on the observations of increased physiological activity and to conclude that this is solely
attributable to attempted deception, in the face of other reasonable or plausible explanations i.e. stress and
anxiety. There is therefore criticism of the accuracy rates of both tests, which may be as low as 50% making it no
more accurate than tossing a coin.
Another type of test is the Truth Verification Test (TVT). It analyses stress in the voice when the person being
questioned answers. The test is usually conducted by the use of a Computer Voice Stress Analyser (CVSA),
which detects micro-tremors and changes in the voice when anxiety is present. An increase would indicate
deception. The test relies on the use of irrelevant questions (known truths), control questions (known lies) as well
as relevant questions pertaining to the issue in question. Following a result of an increase in the response, follow
up interviews are conducted to determine if any other factor could have been present which would account for an
increase in the anxiety level. Commissioner Gill Loveday in her article (Polygraph Tests – Where Does The Truth
Lie? 2001; 2, 3,4) notes that “the control question technique used in polygraph testing is based on the
fundamental premise that a truthful person will respond more (show greater physiological response to) the control
questions, whereas, the guilty person will respond more to the relevant questions. The test assesses the
individual’s credibility by looking for a different reaction between the two types of questions. The underlying
rationale being that people will channel their fears and anxiety to what they perceive as the biggest threat”.
PRE EMPLOYMENT AND EMPLOYMENT TESTING
There has been a marked increase in South Africa regarding the use of polygraph use in pre employment and
employment screening, the use of which is similar to that in use in the criminal justice setting. The difference is
that in employment settings the application is mostly event free, whereas in the criminal justice setting it is event
orientated. The CQT is used regarding events whilst the RIT is used to identify general truthfulness, not based on
a specific event. Although it is clear that very little reliance is based upon the RIT as empirical research has
proven it to be seriously flawed, inaccurate and having little value, it is still most frequently used. A mutual
problem facing both tests is that of “base rate”. What this translates to is the fact that in the relevant population,
the types of behaviour, which the employment screening aims to protect against, occurs in a very low frequency.
David Raskin comments on this problem as follows: “It is estimated that approximately two-million people each
year are given employment polygraph tests in the United States … even with the generous assumption of 85%
average accuracy for [polygraph] tests, approximately 320 000 honest people would be denied employment
because of false positive errors. 1986; before the Employee Polygraph Protection Act”. Due to a majority of
consensus amongst scientists in the USA, there is no acceptable degree of confidence in the use of polygraph
test in employment screening. Hence the need to legislate the situation, and in 1998 the Employee Polygraph
Protection Act 1998, was promulgated. Colin Tredoux and Susan Pooley suggest that similar legislation be
introduced in South Africa. This is necessary as the trust and reliance on such testing is unfounded but widely
being used and on the increase. They are of the opinion that the “current wave of enthusiasm in South Africa for
polygraph based tests of deception is fundamentally misplaced (Polygraph Based Testing of Deception And
Truthfulness: And Evaluation and Commentary (2001): 22 ILJ 819)”.
Apart from the Employee Polygraph Protection Act (USA), there are twenty states which have enacted legislation
designed to control the use of polygraphs by employers, but does not prohibit its use in all settings. An example
of such would be “No employer may require a prospective or current employee to take a polygraph examination
as a condition of employment or continued employment (‘n d’ Polygraph Service: Regulation of An Employers
Use of Polygraph Examinations: 1).”, but there would be exceptions for testing of certain occupational groups for
example, employees working with the manufacture, distribution or dispensing of drugs. The EPPA basically
prohibits most of all pre-employment polygraph testing and four of its exceptions are:
1) use to aid in investigations of incidents involving economic loss or injury to the employer’s business – the
employee must however have access to the property being the subject of the investigation as well the employer
having a reasonable suspicion of such employee;
2) use in investigations involving theft, loss or diversion if the employer is involved in the manufacture, storage, or
distribution of controlled substances. There is however no need for the employer to have a reasonable suspicion
of a specific employee;
3) use in pre employment screening where the employers primary business is the provision of certain types of
security services, where the specific employees will be employed to safe guard sensitive businesses, assets or
institutions; and
4) use in pre employment screening where employers are involved in the manufacture, storage or distribution of
controlled substances and the employee will have direct access to the controlled substances. The American
Polygraph Association has regulated also to a degree what types of questions my or may not be asked at testing.
Personal and intrusive questions are disallowed as well as questioning in the following areas: religious beliefs,
beliefs or opinions on racial matters, political beliefs, beliefs, affiliations or lawful activities regarding unions or
labour organisations and sexual preferences or activities.
In South Africa it has become apparent for a need to promulgate similar protective legislation. This is because
both in the private and public sectors, application of polygraph tests have been used to blanket screen
employees, for extracting confessions, dismissing people who refuse to take the test as well as reducing
insurance premiums making the selling of such policies more attractive. It has been suggested that the Health
Professionals Council of South Africa (HPCSA) should consider the issue of qualification, accreditation and
statutory registration of examiners as in 1999 the Council established that the testing is unreliable and not
suitable for workplace usage.
HOW THE COURTS AND THE CCMA DEAL WITH POLYGRAPH TESTING
CCMA Commissioner, Gill Loveday’s article deals with an overview as to the approach of the Court’s and
Commissioners when dealing with polygraph tests as evidence. Initially, decisions in the Industrial Court
cautioned against the reliance upon polygraph tests as evidence. In Mahlangu v CIM Deltak (1986): 7 ILJ 346
(IC), it was held that a voice analysis test administered by an unregistered psychologist was unscientific, invalid,
unethical and unlawful. The approach to polygraph evidence by commissioners is varied as some find the results
unreliable and therefore inadmissible as evidence, others disregard the evidence if the polygraph examiner fails
to submit his qualifications. There are still conflicting awards concerning the admissibility of expert opinion
evidence of the polygraph examiners pertaining to whether in the absence of other evidence, the results are
conclusive on their own. Some commissioners find that if there is no corroborating evidence supporting the
results, the evidence is inadmissible on its own, others however have accepted the results without any other
supporting evidence, and there are those are satisfied in allowing such evidence if there is other supporting
evidence. It is clear though that everyone accepts that great caution should be exercised when dealing with the
admissibility of such evidence. In Sobiso & others v Ceramic Tile Market (2000): 22 ILJ 811 (CCMA) the
discharging of the onus placed on the employer in terms of section 192 of the LRA is not discharged by sole
reliance on the test results of a polygraph. Therefore polygraph test results are insufficient, in and of themselves
to establish guilt and it can therefore be said that results of such tests cannot be the sole and only indicator of
guilt, other corroborating evidence must be present before reliance can be place on such evidence for a guilty
finding.
Apart from considering the possible promulgation of protective legislation similar to that in the United States, it
may be of considerable use to create guidelines for CCMA commissioners regarding the admissibility, reliability
and weight given to polygraph test results in arbitration proceedings and in this way begin a process of uniformity
and clarity in the way this evidence is viewed and applied.
ACKNOWLEDGEMENTS
(Loveday, G. 2001. “Polygraph Tests – Where does the Truth Lie?” Labour Law News NMG-Levy Consultants
and Actuaries, 10 (5): 2 – 6; Pooley, S & Tredoux, C . 2001. “Polygraph Based Testing of Deception and
Truthfulness: and Evaluation and Commentary” 22 ILJ: 819; “anon. n.d.” “Polygraph Service IQM, Inc: Are
Polygraphs Valid and Reliable; As a Pre-employment Test; Regulation of an Employer’s Use of Polygraph
Examinations; The International Association of Chiefs of Police Establish a Model on Polygraph”; What is a
Polygraph; What is the Process; What the Examiner Cannot Ask; all from the website
http://www.polygraph.to/index.html.)