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The Truth about Polygraph

And How Does It Work?

Human Body

The truth is that polygraph works.


The polygraph remains the most important scientific technology for credibility assessment (lie detection). And while lies cannot be detected or measured in the same way as physical things, many studies have shown that when using modern, evidence-based techniques, a polygraph examination can achieve accuracy rates that are significantly greater than chance. Modern polygraph instruments can make use of today's powerful computers to perform test administration, signal processing and complex data analytic tasks with a level of standardization and consistency that was previously unknown.

Myth: A polygraph test is too subjective.

Fact: The testing and analysis phases of a polygraph test are structured and standardized.

A polygraph test consists of a structured or semi-structured interview, during which the examination topic and test questions are clarified and reviewed, along with the data acquisition and data analysis phases of the examination. Technology solutions are increasingly used to ensure the consistent application of validated polygraph techniques. For example, conducting the test using a standard automated voice or using agorithmic means of analysis.

What Does It Record?

Cardio Cuff

Relative Blood Pressure Changes


Changes in Movement Associated with Breathing


Changes in Skin Conductance or Resistance



Myth: Nervousness, stress, and anxiety can affect the test outcome.

Fact: The polygraph test is not a test of nervousness, stress, or anxiety. Nervousness and stress are normal human experiences and are somewhat understandable during polygraph testing.

Anxiety can include a variety of behavioral health symptoms, and persons with anxiety may benefit from help from professionals with expertise in this area. Fortunately, the polygraph test is not an anxiety detector. Polygraph testing is based on a combination of physiological signals and psychological factors including emotion, cognition, behavioral experience, episodic memory, and more. Polygraph data analysis and polygraph results are based on changes in physiological activity, in response to several presentations of the test stimuli, in comparison to the individual's baseline or normal physiological levels and normal physiological responses.

Polygraph Examination

Are Polygraph Exams Legal?

Yes, the polygraph is a legal investigative tool.

A polygraph exam is commonly used to establish credibility during legal and other investigations. Polygraph exams are not conducted without the consent of the examinee. Whether the polygraph results are admissible in court is dependent on individual state/provincial laws. Many federal and state courts accept evidence of polygraph results where the parties, prior to administration of the polygraph examination, stipulate to its admissibility, and the use of polygraphs for government employee screening has been upheld by the courts and has been successfully cited by federal, state and local governments in defense of claims against them for improper or negligent hiring. (APA 2023)

Myth: A polygraph test is biased against truthful examinees.

Fact: Using modern methods of testing and analysis, evidence points to a decision accuracy in over the 80th or 90th percentiles, depending on the application.

Older polygraph methods have been found to optimize test sensitivity over test specificity and were subjected to criticism regarding bias against innocent persons. Modern evidence-based polygraph methods can be conducted in ways that are optimized for unbiased test sensitivity and specificity.

Where is Polygraph Used?

Polygraph is used in many professions in criminal and investigative settings.

From law enforcement and intelligence agencies to the private examiner, polygraph is used for a multitude of purposes. It is a powerful investigative tool to help establish credibility. In fact, the US government alone employs as many as 1000 federally-certified examiners. (APA 2023)

Law Enforcement
Private Examiners
Intelligence Agencies

Myth: An Internet search yields enough information to "beat a polygraph test."

Fact: Multiple scientific studies have proven that knowing information about the polygraph and execution of countermeasures is not sufficient for tampering with the exam.

Despite what Internet "experts" may say, evidence from these studies contradicts the effectiveness of any approach. More information about these studies is available from the American Polygraph Association.

Myth: The polygraph cannot measure or detect lies.

Fact: All types of scientific tests rely on proxy signals and statistical methods that quantify things that cannot actually be detected or observed with deterministic perfection.

The polygraph works not because it can actually measure or detect lies, but because lying during a polygraph test is associated with subtle though predictable changes in physiological activity. And although all physiological activity is associated with multiple forms of human activity, many studies have shown that when using modern, evidence-based techniques, a polygraph examination can achieve accuracy rates that are significantly greater than chance.

Through ongoing research and education, Lafayette Instrument is dedicated to continuing scientific discovery and adoption in the polygraph community.

LX6 Polygraph

The Lafayette Advantage

Learn more about the Lafayette series of polygraph systems. The pinnacle of development. No one does it better.

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Interested in becoming a Polygraph Examiner?

Join us at PEAK Credibility Assessment Training Center. Contact us to learn more!

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