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FREQUENTLY ASKED QUESTIONS (FAQS)

Polygraph Basics

The term “Lie Detector” is a term of convenience.  It is not a scientifically accurate description of polygraph. Polygraph does not measure lies per se. There is no unique response when most people lie. Meaning that there is not something that generally happens only when people are lying that does not happen at some other time for some other reason.  Anger, embarrassment, fear and other emotions or memories can cause responses.  This is when an experienced well trained polygraph examiner plays a critical role at arriving a correct determination.

 

What does Polygraph Measure?

Polygraph measures an array of physiological responses to a sequence of stimuli that we examiners commonly refer to as a person’s level of arousal.  Most often a person’s level of arousal or their physiological responses are measured by recording chart data that usually includes tracings of relative blood pressure, heart rate, respiration, electrodermal activity, blood volume and pulse while there is simultaneous monitoring for distortions caused by voluntary movement.

 

Usually sequenced stimuli are presented in the form of structured and reviewed question formats. Meaning scripted question and answer exchanges. Sometimes sequenced stimuli can be in the form of photographs.

Physiological response measurements, commonly referred to as polygraph chart data are collected, evaluated and numerical values or scores are assigned if the chart data is stable and interpretable. Those numerical values or scores are referenced to recommended cut scores that are based on published research.  Findings are based on achieving or exceeding those cut scores. From the cut scores a statistical probability of error or an estimated confidence level can be determined.

 

How accurate is polygraph?

Our general answer is we are about 95% sure that polygraph testing overall is about 90% accurate.

Polygraph stand alone has similar if not superior accuracy for discerning deception than horizontal gaze nystagmus or standard field sobriety tests have for detecting alcohol intoxication.  Polygraph is not infallible but is often far more reliable and certainly more objectivate than any one person’s guess or feelings about another person’s truthfulness.  In a survey of wrongful convictions that were later overturned due to exoneration when polygraph was employed somehow, polygraph correctly predicted innocence 82% of the time.

 

Critics of polygraph often cite and misquote the National Academy of Sciences 2003 Publication Polygraph and Lie Detection when opining about polygraph reliability.  Commonly what is misunderstood is that National Academy of Sciences study was focused on multi-issue polygraph used by the federal government for national security purposes, meaning identification of spies. That 2003 National Academy of Sciences study did not focus on specific event or issue polygraph used by law enforcement in criminal investigation.  However, the study did conclude “polygraph tests can discriminate lying from truth telling at rates well above chance, though well below perfection.” Further that study opined that polygraph administered for a specific incident, issue or event examinations would be inherently more accurate than multi-issue exams which the National Academy of Sciences study had focused on.

 

Is polygraph evidence admissible?

Polygraph admissibility varies from jurisdiction to jurisdiction. Some states ban it completely; others allow results by stipulation; and some allow polygraph evidence over objection.  It is admissible in New Mexico and Federally in the 11th Circuit.

 

In Maine polygraph is not admissible in a criminal trial but has been and is often considered at bail and sentencing hearings and in matters related to sex offender probation violations and revocations.

 

Who is suitable for polygraph testing?

Generally persons that have a functional maturity of a Mean Age Equivalence (MAE) or Standard Age Score (SAS) is equivalent to that of a youth age 12 years or older, as determined through standardized psychometric testing (e.g., IQ testing, achievement and/or adaptive functioning), or when there is reasonable certainty the person is not functionally or developmentally impaired (e.g., developmental disorder, learning disorder, or serious emotional disturbance).

 

Specifically to be suitable for polygraph examination a person must have or possess:

 

Adequate abstract thinking, as demonstrated by awareness of the context of the examination referral (i.e., reasons for the testing);

 

Insight into their own and others’ motivation, as demonstrated by the ability to express basic reasons for being honest or dishonest and the basis for the concerns of the referring professional or retaining persons.

 

A basic understanding of right from wrong, as demonstrated by an ability to verbalize potential reasons for being honest or dishonest, and the potential consequences for dishonesty or truthfulness;

 

Understanding of the difference between truth and lies, as demonstrated by the ability to recognize, describe or identify incidents, circumstances, or examples of lying and dishonesty;

 

Ability to anticipate rewards and consequences for lying and behavior, an ability to verbalize potential rewards and consequences for honesty or dishonesty to the examination questions or other contexts; and

 

Ability to maintain consistent orientation to date, time, and location, as demonstrated by independent functioning sufficient to transport oneself to the examination location at the scheduled date and time. (Examiners should rely on professional information sources to determine orientation or disorganized functioning when examinees are residing in or transported from institutional or secured settings.)