Throughout history there have always been problems in ascertaining the truth. In the 1500-1600’s the truth was verified by means of threat, promise and in some cases torture. However, the justices of the era soon realised that admissions gained could not be relied on because of the ways in which they were obtained, and consequently they later rejected evidence gathered in this way.

By the 1700-1800’s the admissibility and methods of verifying the truth had been modified. However, English judges were still loath to receive some confessions into evidence due to the fact that the accused at that time had no right to legal counsel, nor right of appeal. By the beginning of the 1800’s the judges had changed their attitudes to such an extent that all confessions were considered suspect, and as a result were repudiated if the slightest doubt existed

The problems associated with these early methods of verifying the truth led to the contemporary twentieth century methods of recording statements made by suspects, witnesses and complainants alike. Whilst technical advancements have been made in electronically recording the investigative process, little has been available to enhance the interview and interrogative procedures used in determining the veracity of statements. For years attempts have been made to find an approach which successfully differentiates between truth and deception. These have included the use of hypnosis, truth serums and voice analysis, but with few positive results. Only the polygraph, after more than 100 years, has stood the test of time.

In the absence of confessional or other corroborative evidence problems exist in determining whether an individual is telling the truth, or has any knowledge relating to a specific issue or offence. A number of homicides, rapes, abductions, extortions and other serious crimes remain unsolved due to a lack of substantive, or verifiable leads.

Polygraph definition

A polygraph is an instrument that records certain physiological changes in a person undergoing questioning in an effort to obtain truth or deception. A polygraph simultaneously records a minimum of respiratory activity, galvanic skin resistance/conductivity and cardiovascular activity.

In 1961 Davis presented three hypotheses to explain the effectiveness of the polygraph technique. One of these concepts related to fear of consequences. When a subject recognises that he or she faces negative consequences for their actions i.e. imprisonment, financial loss or embarrassment if a deception is discovered, he or she becomes fearful of that outcome. This emotional reaction activates the Autonomic Nervous System (ANS) and such changes are monitored and subsequently recorded.

Polygraphy or psychophysiological detection of deception is based upon a scientific theory that can be tested with the methods of science. Any conscious effort at deception by a rational individual causes involuntary and uncontrollable physiological responses which include measurable reactions in blood pressure, peripheral pulse-amplitude, breathing and electrodermal response. The most commonly used techniques for the psychophysiological detection of deception are control/comparison question tests. The control question test (CQT) assesses a person’s credibility by looking for a differential reaction between two questions: the relevant and comparison questions. It has been shown that a person will develop a “psychological set” and direct their attention to the question that posses the greatest anxiety, concern or threat to his/her well being.

Current Usage

Polygraph testing is currently being used in more than 50 countries in the fields of corrections, criminal investigations, intelligence/counter intelligence and civil matters. In the United States alone all federal law enforcement agencies either employ their own polygraph examiners or use the services of examiners employed in other agencies. Examiners and quality control programs exist in the FBI, US. Secret Service, US Army CID, US Marine Corps CID, Air Force OSI, Navy NCIS, US Customs, US Marshals, Defence Criminal Investigation Service, Internal Revenue Service, US Capitol Police, Food & Drug Administration, Department of Energy, Central Intelligence Agency, Police & County Sheriff’s departments, sex therapists and numerous other investigative bodies.

Law enforcement agencies using the polygraph do so predicated on the basis that it is an important investigative aid, but not a substitute for standard investigative techniques. For decades the law enforcement community has used polygraph testing as an investigative aid to: verify the statements of victims; establish the credibility of witnesses; evaluate the truthfulness of suspects and to help exonerate the innocent who is surrounded by circumstantial or uncorroborated evidence. During 1996, the US Department of Defence conducted over 12,000 polygraph examinations. In recent years the US Department of Defence has used the polygraph in 95% of criminal investigations pertaining to crimes for which the maximum penalty is 15 years or more. Such use accounted for the army solving 64.7% of felony cases compared with the national average of 19.5%

Polygraph technology is now also gaining acceptance in Sex Offender Treatment Programs when testing convicted serial sex offenders whilst on parole or probation. Today a very high number of pedophiles on probation in the states of Oregon and Washington are currently under polygraph surveillance and maintenance programs as part of their parole conditions. The success of the Jackson County Sex Offender Treatment Program (JCSOTP) in Oregon has been so great that other states including California, Texas, Tennessee, Florida, Massachusetts, Indiana and Colorado have adopted the use of polygraph examinations in the supervision, treatment and monitoring of sex offenders on parole and probation.

Legal Aspects

The polygraph examination is, and can only be, a voluntary process. Major technical and computerised advances in technology have been made in the field of polygraphy in the last decade. The development of Zone of Comparison Testing (ZCT) formats, control questions, and validated testing procedures together with ongoing training and research into the validity and reliability of such testing has continued to enhance the utility of the science. This has led to the admission of polygraph results into evidence in all Federal Circuit Courts in the USA, and into 36 of the 50 US States on a stipulated bases (where defence and prosecuting attorneys agree to its admission). In 1989, the US Eleventh Circuit Court of Appeals stated “…based on what it considers to be significant progress in the field of polygraphy in recent years, …it now takes the position that such evidence is generally accepted in the scientific community.”

Supporting the legal use of the polygraph in criminal investigations, legal author and expert on the common law, Wigmore (1970), noted three probative uses of the polygraph with respect to criminal investigation, namely:

  • The observer may use it as a clue to obtaining external data which can otherwise be used in evidence;
  • The disclosure of the lie may impress the subject with the apparent futility of trying to conceal the facts, and may thus lead to a voluntary confession before trail; and
  • The recorded curves may reveal a general emotional consciousness of guilt… and can serve to guide police investigators in their hypotheses.

The United States Supreme Court has held that a Miranda warning before a polygraph examination is sufficient to allow admissibility of a confession that follows an examination. In most courts in the United States that admit polygraph evidence under stipulation the trier of fact has to weigh up the probative value of the matter against the prejudicial effect upon the defendant.

Professor David Lykken PhD from the University of Minnesota has written that “Judicious use of the polygraph in the criminal investigation context not only can improve the efficiency of police work but could also serve as a bulwark to protect the innocent from false prosecution. In fact, I believe that the police use the polygraph too infrequently… if used wisely, polygraphing can greatly facilitate police work.”

Within the Australian context there are no legal impediments to the use of polygraph testing as an investigative tool other than the Lie Detectors Act NSW 1983 which prevents testing in certain circumstances.

Validity and Reliability

In the past 75 years over 250 studies have been conducted on the accuracy of polygraph

testing. Since 1980, 10 separate studies based on 1,909 real cases showed that the accuracy rate for truthful subjects was 97% and for deceptive subjects, 98%. There have been more published studies done on polygraph accuracy, validity and reliability than on handwriting analysis which is routinely admitted into evidence on a daily basis.

Although sceptics of polygraph techniques have expressed concern that polygraph testing is not 100% accurate one needs to consider that there is no one scientific technique in dealing with humans that is 100% accurate including psychiatry and psychological assessments regarding clinical diagnosis. Classification of psychological disorders, although subjective, are often challenged by other experts and, at times, incorrectly diagnosed. Cross contamination has occurred in DNA testing, fingerprints have been wrongly classified, handwriting evidence has been misinterpreted and eye witnesses make mistakes. Furthermore, admissibility does not necessarily mean that evidence is valid. Note how invalid eyewitness and psychiatric findings can be, and often are, legally and judiciously recognized as admissible evidence.

Comparative Investigative Techniques

In 1978 a study by Drs. Horvath &

Widacki was conducted which compared the polygraph with handwriting analysis, eyewitness identification and fingerprints. A group of 80 students was divided into 20 groups of four persons. A mock crime was then committed by one student in each group and the abovementioned investigative means were employed by experts in each field (in the case of the eye witnesses, they had been told they would be eyewitnesses to a crime prior to the experiment) to try to correctly identify the offender in each group. The results were as follows:

Identification  Correct    Incorrect    Incon.

Polygraph             18            1                1

Handwriting          17            1                 2

Eyewitness            7             4                9

Fingerprints          4             0               16

These figures clearly demonstrate the effectiveness of the polygraph as an investigative tool.

Current usage within criminal & private investigations.

Polygraph usage has proven successful in:

  • Eliminating suspects
  • Recognising false complaints
  • Testing informants to determine the veracity of information provided
  • Providing a new “key” to an investigation when all other standard investigative techniques have been exhausted
  • Narrowing the focus of enquiry
  • Gathering additional information and evidence
  • Assisting to focus the investigation on particular suspects

In one interesting case which involved a polygraphist with the Oregon State Police USA investigating a theft a polygraph was used to conduct a searching peak of tension test. It was learned that the suspect’s wife had mysteriously disappeared but he claimed that she had returned to her family in Mexico. When a control question technique showed him to be responding deceptively in this matter, a Peak of Tension Test was administered to determine if the location of the body could be discovered. The first searching peak asked the following questions:

  1. Is your wife’s body in the river?
  2. Is your wife’s body by the railroad tracks?
  3. Is your wife’s body in the potato field?
  4. Is your wife’s body by the farm buildings?
  5. Is your wife’s body by the house?

When strong autonomic reactions occurred in response to question 4, the man was presented with another series of questions worked in a similar manner but relating to the specific farm buildings. Large responses were found to questions associated with the shed. While spectators waited in suspense, a bulldozer cleared the area around the building where his wife’s body eventually was found. Dramatic results have also occurred whist looking for weapons and other exhibits used in a crime. Another case in point was the murder of two girls, Kynara Carreiro and Krisin Wiley, aged seven and ten years respectively, in Houston, Texas in 1992. A 34 year old neighbour, Rex Mays, had long been suspected of stabbing and slashing the two girls to death, but there was insufficient evidence to charge him. Mays consented to a polygraph examination, and when told that he had failed the test, Mays confessed.

In the infamous Sharon Tate murder case, the Los Angeles Police Department administered polygraph examinations to William Garretson, the 19 year old caretaker, and to Sharon Tate’s husband, Roman Polanski. Both passed the tests which showed they had no knowledge of, or involvement in the murders, Police continued the investigation which resulted in the arrest and conviction of Charles Manson and members of his “family”. The Los Angeles Police Department Scientific Division which incorporates the Polygraph Unit has 5 qualified polygraph examiners. The work load of this unit consists mainly of major felony cases including homicide and child sexual abuse investigations.

Other uses within the private sector include:

  • Professional misconduct allegations e.g. Doctors, Accountants etc.
  • Theft/Fraud investigations
  • Civil investigations
  • Testing the veracity of affidavits/statements
  • Investigating malicious and false allegations
  • Unfair dismissals
  • Drug usage by athletes
  • Disputes of fact
  • Sexual harassment claims/allegations


Although the polygraph is not a panacea for every investigation it has proven to be an effective investigative tool, especially in the absence of other corroborative evidence. Veteran US District Attorney, Peter Sandrock Jr., wrote recently in regard to the polygraph, “…the results are not infallible, but they are far, far more reliable than our subjective intuitions. Because of the polygraph, we are better prosecutors and guarantors of justice”. Internationally the polygraph will continue to greatly enhance the investigative process as another weapon in a growing arsenal of investigative and scientific tools available to investigators.

Abrams, Stanley (1996) A foundation for Polygraphy, unpublished, Portland, OR P 33
Polygraph Issues and answers: American Polygraph Association February 1, 1996
Davis, R.C., Physiological responses as a means of evaluating information in A.D Biderman & H. Zimmer, eds., The manipulation of Human Behaviour (New York: Wiley, 1961)
American Polygraph Journal Volume No. 26, Number 2, 1996.
Barland, Gordon (1997) Federal Use of Polygraph, unpublished, US Department of Defence
A recidivism study of 173 sex offenders conducted by Charles Edson, Parole and Probation Officer and Sex Offender Specialist for the Medford Department of Corrections, Oregon, 1991.
Van Aperen, Steven (1998) Polygraph surveillance and disclosure testing of pedophiles and sexual offenders released on parole/probation (unpublished) paper presented to the Hon. Jeff Kennet, Premier of Victoria.
Wigmore J. (1970) Wigmore on Evidence, Vol. III, 687-867, Chadbourn Revision, Little Brown and Company.
US Supreme Court: Wyrick v. Fields, 103 S.Ct 394 (1982)
Polygraph Issues and Answers, American Polygraph Association Revised Ed. February 1st, 1996.
Dr. Norman Ansley (1990): The validity and reliability of polygraph decisions in real cases
Polygraph 19(3): 169-181.
Widacki J, & Horvath, F. (1978) Experimental Investigation of the Relative validity and utility of the polygraph technique and three other methods of criminal identification
Abrams, S. A polygraph handbook for Attorneys (Lexington, Mass.: Heath, 1977)
Ortiz, Roy, Officer in Charge, Polygraph Unit, Los Angeles Police Department.
Special thanks to Det. Sgt Paul Bergin, Queensland Police Service for the use of his article: The use of polygraph in the Queensland Police Service.