HOW DOES THE POLYGRAPH WORK?
During examinations, attachments are placed on the examinee which record the sympathetic reactions to the autonomic nervous system. The sympathetic nervous system automatically responds to any kind of emergency received by the senses and without the concurrence of will. When someone is asked a question where the truth has a degree of consequence, the sympathetic nervous system is stimulated and causes involuntary physiological changes that can be recorded, measured, and analyzed.
The polygraph is a scientific tool that measures physiological phenomena including: breathing, galvanic skin resistance, and cardiac activity.
A polygraph does not detect a lie so much as it verifies the truth.
TRUTH VERIFICATION
“To tell the truth” and to “prove a person is truthful,” have been two of the most pressing, fundamental issues in human existence. We have been interested for centuries in the ability to verify truth and truthfulness.
Early primitive cultures attempted to determine if a subject was telling the truth by using a theory known as Trials by Ordeal, which were physical tests involving exposure to fire and water. The presumption was that the innocent would be protected and would not suffer harm. The Code of Hammurabi in 2100 BCE directed a person accused of sorcery to be thrown into a sacred river. The thought was if a subject drowned he/she was punished by the gods. Inversely, during medieval witch trials, a similar process was used, but if a subject drowned it was believed that they had been truthful.
As time passed, intelligence evolved and technology and science flourished. Modern day polygraph instrumentation and techniques emerged, applying scientific methods to record and measure “human physiological responses.” It is a demonstrable fact these recordings of physiological changes serve as a basis for reliable diagnoses of truth or deception.
F.A.Q.
COMMONLY ASKED QUESTIONS ABOUT POLYGRAPH TESTING
“Tests conducted by the US Department of Defense report a specific issue examination, using validated examination formats, has an accuracy range of 93% – 95% (independent studies suggesting even higher scores).”
“Research studies published in the Journal of Forensic Sciences, Vol. 23, July 1978 reported the utility and validity of the polygraph technique in comparison to fingerprint identification, handwriting analysis, ballistics, serology and eyewitness identification with the following results:
POLYGRAPH 95%
SEROLOGY 85%
BALLISTICS 76%
HANDWRITING 72%
FINGERPRINTS 59%
EYEWITNESS 54%”
A:
According to Nelson (2015): Event specific diagnostic exams are shown to have a mean unweighted accuracy rate of .89 (95% CI = .82 to .95), while exams interpreted with the assumption of independent response variance are shown to have a mean accuracy rate of .82 (95% CI = .74 to .90). (p.321)
A standard polygraph examination typically involves two (2) to four (4) test questions regarding the issue being investigated.
The time depends on several variables, such as the type of issue/offense being explored and the complexity of circumstances. Typically, an examination ranges from 2-3 hours, but some can take even longer. For us, accuracy trumps time.
The general rule in Indiana is that even in a criminal trial the examination results are allowed when a specific agreement has been reached by the defendant, his attorney, and the prosecuting attorney to have the examination findings introduced into evidence. Prosecutors often reconsider the advisability of prosecuting a case when the defendant has successfully passed a polygraph test administered by a reputable examiner. Polygraph examinations are routinely ordered by the court in clinical sex offender monitoring, and results that are positive for indications of deception can be the basis for a probation violation. Case law has allowed test results in Indiana regarding civil cases and administrative hearings.
Not at all. Infallibility has never been found in any science which deals with human beings. Polygraphs record physiological responses to a series of questions presented to an individual by a qualified examiner using validated testing formats. The examiner is then able to decipher the chart polygrams, analyze the recorded test data and render a reproducible opinion as to the veracity of the subject being tested. When there is quantifiable doubt of the validity of the test results, the examiner will consider the test as “inconclusive” and may recommend reexamination to resolve the inconclusive outcome.
Questions concerning sex habits have no place in a polygraph UNLESS sex is the relevant issue of the examination. Examiners are dedicated to treating all examinees with dignity and respect regardless of the potentially sensitive nature of an examination.
A reasonable amount of nervous tension is perfectly normal. It will not be mistaken for deception. Nervousness is normal and it does not prevent the examiner from distinguishing between truth and deception. General nervous tension is part is part of the examinee’s physiological baseline and its presence in not diagnostic. During an examination, sensitivity to unresolved issues of importance to the examinee causes physiological reactions. This should not be confused with general nervous tension that appears everywhere during the examination.
No. High blood pressure does not cause the pattern results of an untruthful person.
NO! No trickery is involved, no surprise questions are asked. You will know every question on the test because all of the questions are reviewed prior to the examination to clear up any confusion or misunderstandings. The test requires only “yes” or “no” answers.
No, there is no possibility of electrocution. You may, however, feel pressure from the blood pressure cuff.
Feeling responsible is not the same as being responsible. Proper questioning will resolve this.
Our examiners utilize advanced computerized instruments for Psychophysiological Detection of Deception (PDD) credibility assessments. We strive to provide the most up to date and progressive testing methods available.
According to the American Polygraph Association (APA) (2011):
A dimensional profile of criterion accuracy was calculated for each PDD technique, including the unweighted average of the proportions of correct decisions for deceptive and truthful cases, excluding inconclusive results, along with the unweighted average of the proportions of inconclusive results.13 Results were aggregated for techniques that satisfy the APA 2012 requirements for evidentiary testing, paired testing, investigative testing, and for all PDD techniques included in the meta-analysis. Excluding outlier results, comparison question techniques intended for event-specific (single issue) diagnostic testing, in which the criterion variance of multiple relevant questions is assumed to be non-independent,14 produced an aggregated decision accuracy rate of .890 (.829 – .951), with a combined inconclusive rate of .110 (.047 – .173). Comparison question PDD techniques designed to be interpreted with the assumption of independence of the criterion variance of multiple relevant questions, produced an aggregated decision accuracy rate of .850 (.773 – .926) with a combined inconclusive rate of .125 (.068 – .183). The combination of all validated PDD techniques, excluding outlier results, produced a decision accuracy level of .869 (.798 – .940) with an inconclusive rate of .128 (.068 – .187). Data at the present time are sufficient to support the polygraph as highly accurate, but insufficient to support an assertion that PDD testing can provide perfect or near-perfect accuracy. (p. 200)
13 The unweighted average was considered to be a more conservative and realistic calculation of the overall accuracy of all PDD examination techniques. Calculation of the weighted average, or the simple proportion of correct decisions, often results in higher statistical findings that are less robust against differences in base-rates and therefore less generalizable.
14 Independence, in scientific testing, refers to assumptions about whether external factors that affect the criterion state of each question (i.e. truthfulness about past behavior) is assumed to affect the criterion state of other questions. In PDD testing, the results of multi-facet and multi-issue exams are interpreted with decision rules based on the assumption of independence, while the results of event-specific single-issue examinations are more often interpreted with decision rules based on the assumption of non-independence.
Credibility Assessment/ ~
According to Raskin and Kircher (2014):
Honts (2004) reported that 11 high-quality published laboratory studies of the CQT indicate that the CQT is an accurate discriminator of truth-tellers and deceivers. Overall, the CQT correctly classified 90% of the subjects, and produced approximately equal numbers of false-positive and false negative errors…(p. 80-81)
(for more detailed descriptions of laboratory studies, see
Ad Hoc Committee on Polygraph Techniques, 2011;
Raskin and Honts, 2002).”
RASKIN declaration/ “G:\Research\PDD Defense\DECLARATION OF POLYGRAPH EXPERT.pdf”
American Polygraph Association. The Ad-Hoc Committee on Validated Techniques. (2011). Meta-analytic survey of criterion accuracy of validated polygraph techniques. Polygraph, 2011, 40(4). Chattanooga, TN: American Polygraph Association.
Krapohl, D. J. & Shaw, P. K. (2015). Fundamentals of polygraph practice. San Diego, CA:Elsevier Inc.
Nelson, R. (2015). 2015 update to the APA 2011 meta-analytic survey of validated polygraph techniques. In Krapohl, D. J. & Shaw, P. K., Fundamentals of polygraph practice (pp. 319-333). San Diego, CA: Elsevier Inc.
Raskin, D. C & Kircher, J. C. (2014). Validity of polygraph techniques and decision methods. In Raskin, D. C., Honts, C. R., & Kircher, J. C. (Eds.), Credibility assessment: Scientific research and applications (pp. 63-129). San Diego, CA: Elsevier Inc.