Does The Polygraph “Lie Detector” Work?

Since human beings first communicated with each other, we have told lies. We have also sought to sort these lies from the truth, and this need became even more critical when societies created legal systems. Law enforcement and other agencies that investigate crimes understand that the human potential to determine truthfulness is limited, but we do have the capacity to create technology that can detect signals beyond our scope. The polygraph was the first truth verification invention that proved we could utilize technology to detect deception—but how does this technology stand up today?

The History Behind The Polygraph

The polygraph became known colloquially as the “lie detector,” but that term is a misnomer. There is no scientifically conclusive way to detect lies, but there are ways to measure psychophysiological reactions caused by the stress of being deceptive. This concept is what led to the polygraph and, later, more advanced truth verification technology such as the Computer Voice Stress Analyzer (CVSA®).


  • In 1878, Italian physiologist Angelo Mosso investigated people’s physiological reactions when being questioned using a device called a plethysmograph to measure respiratory and cardiovascular responses. Other scientists took his research and improved on it.
  • A Canadian psychologist, John A. Larson, developed a version of the polygraph in 1921 while working for the Berkeley (California) Police Department. He christened the device “polygraph” from the Greek “polýgraphos,” which means “much writing.” The polygraph read and charted blood pressure, respiration, and pulse. Leonarde Keeler further contributed to the device in 1938, adding sensors to measure galvanic skin response.
  • The current polygraph model works basically the same way as those invented close to 100 years ago by measuring these responses through sensors placed on the body—a blood pressure cuff to measure heart rate and blood pressure, pneumograph tubes to measure respiration, and galvanometers attached to the fingertips to measure perspiration.
  • In the late 1940’s, Chicago lawyer John E. Reid further refined the polygraph process. Reid went on to develop the Reid Technique, an interview and interrogation methodology commonly used by law enforcement with or without a polygraph examination.
  • Today’s polygraph is digital, and while it operates on the same premise and sensors as the analog version, it uses an algorithm to evaluate the data and charts it on a computer program.

Polygraph Vulnerabilities

Chicago lawyer William Scott Stewart wrote an article published in the November 1941 issue of Esquire Magazine titled “How to Beat the Lie Detector.” This is probably the first article of its kind focusing on countermeasures against the polygraph, and Stewart pointed out that you could manipulate the polygraph’s results by intensifying your emotions when asked harmless questions. Such “control questions” are asked during the Control Question Test (CQT) and are designed as comparisons to the relevant questions. As for physical countermeasures, Stewart suggested biting the tongue or inside of the mouth or making muscle movements that cannot be seen by the operator, such as moving a toe or flexing a leg muscle.

The polygraph is still vulnerable to both physical and psychological countermeasures and it also suffers from a significant error rate based upon inconclusive, false positives, or false negatives results.

Manipulation During Control Questions:

  • Subjects may control their breathing
  • Contraction of sphincter muscles
  • Biting the tongue or inside of mouth
  • Thinking about horrible things
Former polygraph examiner and Oklahoma City Detective Sergeant Doug Williams was sentenced to two years in prison by the federal government in 2015 for activities associated with his teaching people how to beat the polygraph. After years of using the technology, he came to distrust the results and taught thousands of people to use countermeasures. He rates the accuracy of the polygraph at 50 percent at most. In fact, U.S. government agencies have taught individuals involved in undercover operations to beat the polygraph, thus validating Williams claim that techniques can be taught to defeat the polygraph.
Manipulation During Relevant Questions

  • Practicing relaxation techniques
  • Doing mental calculations
  • Thinking of calming subjects

The Positive Impact of the Polygraph

Despite its flaws, the polygraph set a new precedent for the use of truth verification technology as part of the police interview process and paved the way for future innovations. The polygraph community has a powerful lobby and loyal users. Many of the examiners trained to use this technology are reluctant to reinvent their skills or invest in newer technology, but approximately thirty of the top polygraph studies show this truth verification tool is not as reliable as they would like to believe. Studies have varied results measuring the accuracy of the polygraph, with estimates ranging from 70 to 90 percent accurate. Furthermore, only 29% of 194 “scientific studies” touted as proof by polygraph advocates met the minimum standards of scientific adequacy, according to the 2003 National Research Council report by the Committee to Review the Scientific Evidence on the Polygraph.

Polygraph evidence has been successfully admitted in court, and nineteen states allow polygraph testimony based on conditions unique to each state. This technology has also been used for pre-employment screening in both the public and private sector. A primary benefit of the polygraph is that it can be used to elicit confessions after examinations if subjects believe deception has been uncovered. But in today’s Internet Age, individuals who are subject to polygraph examinations can access information about the polygraph which was once unobtainable and in some cases, restricted from public release. These individuals have begun to turn the tables on the polygraph by understanding its many shortcomings, as detailed on websites such as

Pros Cons
Legacy system with long history of use in law enforcement and military applications. Popular use by the public and reality TV has diminished its reputation.
Use has been challenged in court, but in some cases, polygraph testimony has been allowed. Subject to countermeasures, false positive, false negatives, and inconclusive results.
Cost of technology has decreased due to competition in the marketplace. Accuracy rates can vary from 50 percent to 87.5 percent.
The polygraph process is well-known due to exposure in the media/popular culture. The examination is lengthy and requires a subject to remain still while hooked up to numerous sensors.
The American Polygraph Association has a strong foundation with 2,700 plus members who lobby on behalf of the technology. The polygraph examiner training is expensive and requires a one-year internship, but there is no recertification option to determine continuing compliance.

The Computer Voice Stress Analyzer (CVSA®): The Next Generation of Truth Verification

The Computer Voice Stress Analyzer (CVSA®) was born out of a need to improve the measurement of psychophysiological associated with deception. In 1970, Olaf Lippold discovered the muscle “microtremor.” Based upon this discovery, three former U.S. Army officers formed Dektor Counterintelligence and Security, Inc. and created a technology to measure the “Lippold tremor” in the human voice. This became the first Voice Stress Analysis (VSA) tool.

NITV Federal Services’ founder, Charles Humble, refined this technology and debuted the CVSA® in 1988. This device also measures psychophysiological changes in response to direct questions, but unlike the polygraph, it focuses solely on changes in voice frequency controlled by involuntary muscles. In other words, there is no way for a human to control the reactions measured by the CVSA®. Using only a microphone and the CVSA® instrument, the results are charted to indicate stress associated with “deception” or “no deception.” With the CVSA®, there are no inconclusive results as there are with the polygraph.
In field and lab studies, the CVSA® has proven to have higher accuracy rates than the polygraph. Professor James Chapman (Professor Emeritus, Former Director of Forensic Crime Laboratory, State University of New York at Corning) and Marigo Stathis (neuro-cognitive scientist and research analyst) conducted a study that showed “of the 329 confession possibilities, 92.1% of the CVSA® examinations produced a ‘Stress Indicated’ result, and 89% of those resulted in validated confessions.” And in “96.4% of interviews conducted, where the CVSA® indicated stress, suspects made self-incriminating confessions.”

Pros Cons
No known countermeasures and extremely high accuracy rate, very low error rate, no inconclusive results. Less well-known than the polygraph.
Ease of use, shorter examination time required, strong portability, and requires only a microphone attached to the interview subject. None.
Adaptability of use for analyzing pre-recorded materials or use over phone or Internet. None.
Many polygraph examiners have transferred their skills in truth verification analysis to the CVSA®. Polygraph organizations have campaigned for over 40 years to dissuade polygraph examiners from switching to the CVSA®.

Addressing Many Polygraph Issues with Innovative Technology

The CVSA III® has solved many of the problems relating to the polygraph. Scientific research and advancements in digital technology have allowed for more adaptive uses of CVSA® truth verification technology, more accurate results, and data that is easier to comprehend than the polygraph system. Below, we’ve provided a value comparison between both technologies:


  • > 98% accuracy rate based on scientific field and lab studies
  • Less than ½% error rate.
  • The American Polygraph Association claims an accuracy rate of 87.5% but admits “critics’ of the polygraph calculate the accuracy rate as <70%”
  • Polygraph does not include “inconclusive” results in its accuracy statistics; instead, they eliminate this outcome to artificially increase statistical accuracy rates
  • Only about one third of studies validate polygraph accuracy rates, and most of those are sponsored by polygraph associations and/or funded by pro-polygraph entities
  • Records data through a microphone, thus lending itself to portability, covert use, telephone, and internet or cloud-based applications.
  • Subject’s movements are not restricted during interview.
  • Analyzes pre-recorded material.
  • Easy to read charts that can be explained in layperson’s terms to the subject, scored by a patented algorithm.
  • Less portability
  • Requires a controlled office-like setting
  • Requires sensors attached to chest, arm, and fingers; subject must remain completely still for entire examination.
  • Uses multiple countermeasures sensors, which further complicate the examination process
  • Charts are complicated, open to interpretation, and can only be read and understood by trained examiners.
PHYSIOLOGICAL MEASUREMENTS FM frequencies in the voice Heart rate, blood pressure, perspiration, respiration, and movement detected by countermeasures’ sensors
COUNTERMEASURES No known countermeasures Subject to multiple physical and psychological countermeasures which are well-known online
AVERAGE COMBINED ERROR RATE (FALSE POSITIVE, FALSE NEGATIVE, AND INCONCLUSIVE) Less than ½% 30-40% (based on National Academy of Science data)
(including Dell computer with 4-year warranty and 2 training slots)

$6,400 for system only, training and computer not included.

With training (around $7,500) and computer (around $1,500) total cost approx: $15,400.

  • Two FREE training slots
  • Five days
  • No internship requirements.
  • Recertification every 2 years with a one (1) year grace period if requested.
  • Courses held in various police agencies across the country on a regular basis to ensure minimal additional expense.  
  • $7,500.00 (approximate)
  • Eight weeks
  • One additional year of internship.
  • Students must attend training at specific polygraph training facilities
  • Salary, travel, lodging and meal expenses are very expensive and should be calculated into training costs
INTERVIEW TECHNIQUE DESIGNED FOR TECHNOLOGY Defense Barrier Removal (DBR®) System—a rapport building methodology The Reid Technique—an accusatory method that has led to lawsuits and false confessions.
AVERAGE NUMBER OF EXAMS THAT CAN BE CONDUCTED PER DAY. Four to six (examinations typically last 45-90 minutes depending on the type of examination) Two (examinations are a minimum of 2-3 hours and often longer)
  • Approximately 2,600 police agencies, including California Highway Patrol, Atlanta P.D., Illinois State Police, New Orleans P.D.
  • Dozens of Correctional Facilities, including California Department of Corrections and Rehabilitation and the Missouri Department of Corrections
  • U.S. and Foreign Military
  • U.S. Federal Courts
  • Law Enforcement Agencies (local, state, federal) across the USA and abroad.
  • Various US Government agencies
  • Private sector corporations (Restricted use according to the Employee Polygraph Protection Act of 1988.

Although the polygraph has been the accepted “lie detection” technology for many years, the CVSA® has made significant inroads and is now becoming the new benchmark to validate truthfulness. Many CVSA® Examiners came from the polygraph world and found they could be more effective using this system—they can conduct more examinations, focus on clear results, and show their interview subjects exactly where they were exhibiting stress in response to questions. The polygraph community’s hold on truth verification is waning because they haven’t kept pace with the current data-driven environment where adaptability is key—that means user friendly technology, interconnectedness of applications with other technologies such as mobile and cloud-based systems, and, of course, accurate results. We owe a debt to the inventors of this historical system but also have a duty to recognize obsolescence and continue to develop new technology built on tested scientific foundations.

NITV Federal Services is redefining the field of truth verification for the next generation, and we welcome you to join us on this exciting journey. Our leadership in truth verification training and technology is what turns skepticism into testimonials. Please contact us for more information.