- Reading Time 12:00
Polygraph tests have been used for decades as a tool to detect deception in various settings, from criminal investigations to pre-employment screenings. Despite their widespread use, there is ongoing debate surrounding their accuracy and reliability.
In this article, we discuss the accuracy of polygraph examinations based on our own personal experience. We demonstrate how contradictory and misleading information can be found on the web and in books, and we conclude with our own practical, neutral insights on the numbers behind its accuracy.
Conflicting claims regarding polygraph test accuracy
The American Polygraph Association says that its trained examiners can get an accuracy rate of more than 90%. Its website claims that thousands of its members give polygraph tests around the world every year to protect the public by verifying the truth, while the American Psychological Association says lie detectors don’t work.
The truth is, there is plenty of conflicting evidence swaying in favor of lie detectors and against them. One problem, research shows, is that humans have a tendency to lie from a young age, mastering the “white lie” by age 6. As people grow, some will become pathological liars, which could affect how they react and respond if given a polygraph.
Organizations and scientists studying polygraphs found that it’s difficult to assess how well they work because there are too many definitions of deception. Early theorists believed that deception required effort and, thus, could be assessed by monitoring physical changes.
Since then, studies have found many ways of measuring the results of deceit, and many times they have been deemed “inconclusive.”
A 2003 report from the National Academy of Sciences discovered that after almost a century of research in scientific psychology, there is little basis for believing that a polygraph could have the type of accuracy that the APA claims. Critics say the underlying problem is theoretical since a person’s physiological changes might occur for a variety of reasons other than lying.
For example, studies have shown that individuals from certain cultural backgrounds may have different physiological responses to stress, which can affect the accuracy of the test results. Additionally, individuals who are anxious or nervous may be more likely to produce false positives, while individuals who are highly skilled at deception may be able to produce false negatives.
The examiner’s voice alone could trigger a naturally anxious individual, and an honest person may be nervous when answering truthfully, whereas a dishonest person would not be.
Studies have claimed the accuracy of polygraph exams to be 70–90%, pointing out that only 29% of the results put forward by “polygraph advocates” met the minimum standards of scientific adequacy.
Factors That Can Affect the Accuracy of Polygraph Tests
There are a number of factors that can affect the accuracy of a lie detector test. These factors can range from the physiological responses of the test-taker to the type of questions being asked during the test.
The test is traditionally divided into three segments: the pre-test, the examination, and the post-test. Each of these stages has the potential to affect accuracy.
- One major factor that can affect the accuracy is the emotional state of the test-taker. When individuals are anxious or nervous, they may produce physiological responses that can be interpreted as indicating deception, even if they are telling the truth. Additionally, if the test-taker is experiencing intense emotions, such as fear or anger, they may produce physiological responses that can mask their true response to a question.
- Another factor that can influence the accuracy of a lie detection test is the type of questions being asked. If the questions are too general or ambiguous, it can be difficult to determine whether the test-taker is being truthful or not. Similarly, if the questions are too leading or suggestive, the test-taker may be more likely to provide a false response. In some cases, the wording of the questions may also be culturally biased, which can affect the accuracy of the test results for individuals from certain backgrounds.
- The experience and training of the person administering the test can also affect its accuracy. If the examiner is not properly trained, they may be more likely to misinterpret the test results or make other errors that could affect the accuracy of the test. Additionally, the examiner’s personal biases or preconceptions about the test-taker may also influence their interpretation of the results. For example, an examiner who believes that the test-taker is guilty may unconsciously influence the results by framing questions in a way that is more likely to elicit a deceptive response.
- Age and gender: Studies have shown that older individuals and women may produce more false positives on lie detection tests due to changes in the autonomic nervous system and hormonal differences. However, this effect is relatively small and should be considered in conjunction with other factors.
- Mental or physical condition: Individuals with mental or physical conditions that affect their physiological responses may produce inaccurate results on lie detection tests. For example, individuals with high blood pressure or heart conditions may produce false positives, while individuals with neurological disorders may produce false negatives.
- Different drugs and illegal substances like anti-hypertensive and anti-anxiety medications can influence the accuracy of your polygraph examination by altering physiological responses and impairing cognitive functioning.
- During the examination, you will be attached to several devices. It is the responsibility of the examiner to ensure these devices are securely attached. If they are not, the accuracy could be affected by not reading your physical responses properly.
- If you are highly uncomfortable, this could also affect the accuracy. This scenario could be caused by the examiner or the environment of the polygraph test.
- In the post-test stage, polygraph testing accuracy can be affected if the results are misread. This could happen if the examiner is improperly trained or makes an error in reading the results.
Overview of the results of various studies on polygraph test accuracy
Numerous studies have been conducted on the accuracy of lie detection tests, with varying results.
One of the earliest and most well-known studies on the accuracy of lie detection tests was conducted by John Reid in 1947. Reid tested the accuracy of lie detection tests by asking participants to either tell the truth or lie about a crime they had committed. He found that the tests were accurate in 89% of cases.
Among the most frequently cited studies is a meta-analysis conducted by the National Academy of Sciences in 2003, which concluded that the accuracy of polygraph tests is no better than chance. This finding is based on an analysis of over 80 studies conducted on the use of polygraph tests in criminal investigations and employment screening.
However, more recent studies have produced mixed results. For example, a study conducted by the National Research Council in 2003 found that the accuracy of lie detection tests was between 80% and 95%, depending on the type of test used and the qualifications of the examiner.
Another study conducted by the American Psychological Association in 2012 found that the accuracy of polygraph tests varies depending on the context in which they are used. In situations where the stakes are high, such as criminal investigations or employment screening, the accuracy of the test tends to be lower. In contrast, the accuracy of the test tends to be higher in lower-stakes situations, such as academic research or military screening.
A study conducted by the Department of Defense in 2002 found that the accuracy of the test was only slightly better than chance in identifying deception. This study also found that the use of countermeasures by test-takers can significantly reduce the accuracy of the test.
In a review of the literature on lie detection tests published in the Journal of Applied Research in Memory and Cognition in 2018, the authors concluded that while some evidence supports the use of lie detection tests in specific contexts, the overall accuracy of these tests remains questionable. The authors also noted that there is a need for more research on the accuracy of newer, computerized lie detection tests.
Despite the mixed results of these studies, lie detection tests continue to be used in various contexts, such as criminal investigations, employment screening, and national security clearance.
Explanation of the limitations of this research
While the studies discussed in the previous section provide valuable insights into the accuracy of polygraph tests, it is important to note that there are several limitations to this research that must be taken into account.
- One major limitation is the lack of standardization in polygraph testing procedures across different studies. This can lead to inconsistent results and make it difficult to compare findings across studies. For example, different studies may use different questions, different methods of scoring the test, or different physiological measures to detect deception.
- Another limitation is the use of simulated rather than real-life scenarios. Many studies on polygraph test accuracy have used laboratory-based simulations of deception, which may not accurately reflect the complex and dynamic nature of real-life situations where deception may occur. In addition, participants in these studies may not feel the same level of stress or pressure as they would in a real-life situation, which could affect the accuracy of the test.
- A further limitation is the potential for bias in the studies themselves. For example, researchers conducting studies may have their own beliefs or expectations about the accuracy of polygraph tests, which could affect the way they design or interpret their research. Additionally, studies funded by organizations with an interest in promoting the use of polygraph tests may be more likely to report positive results than studies conducted independently.
Finally, it is important to note that even the most accurate polygraph tests are not foolproof. While some studies have reported high accuracy rates, there are still cases where individuals have been able to deceive the test or where innocent individuals have been wrongly accused based on the results of a polygraph test.
Comparison of the accuracy of polygraph tests to other forms of lie detection
When it comes to detecting lies, the polygraph test is not the only method available. Other forms of lie detection include the following:
- Voice stress analysis: This method analyses changes in the pitch and tone of a person’s voice when answering questions. However, this method has been criticized for lacking scientific validity.
- Micro expressions: These are brief facial expressions that reveal a person’s true emotions. While some experts believe they can be used to detect lies, others argue that they are not reliable indicators of deception.
- Eye-tracking: This method measures the movement of a person’s eyes when answering questions. Some studies have suggested that it can be a reliable indicator of deception, but more research is needed.
- Brain imaging: This involves the use of MRI or fMRI scans to measure brain activity when a person is telling the truth or lying. This method is still in the experimental stage, and more research is needed to determine its accuracy.
- Behavioural analysis: This involves observing a person’s behaviour, such as body language and speech patterns, to detect signs of deception. While this method can be useful, it is not fool proof and can be influenced by personal bias and interpretation.
Overall, the accuracy of these methods varies, and none of them can be considered completely reliable. However, research suggests that some methods may be more accurate than others. For example, a study published in the journal PLOS ONE found that eye-tracking was more accurate than the polygraph test in detecting deception.
It’s also worth noting that none of these methods can detect lies with 100% accuracy. Human behaviour is complex, and people can deceive in a variety of ways. Additionally, factors such as stress, anxiety, and fear can all affect a person’s physiological responses, making it difficult to determine whether they are telling the truth or lying.
Encouraging truth telling
Although the accuracy of a polygraph test cannot truly be measured and concluded as scientific evidence, it is still used by probation officers, law enforcement, and government agencies. But why?
One popular theory is that polygraphs may appear to be accurate because the person taking them believes they work.
Polygraph research has not separated placebo-like effects from the actual relationship between deception and physical responses. If you believe the lie detector works, you may be very nervous and tell the truth when asked. Polygraph exams encourage examinees to tell the truth.
In 2014, forensic psychologist Theresa Gannon studied the likelihood of sex offenders disclosing something of interest when using a polygraph test vs. no test at all. They discovered that with a polygraph, their participants were 75% more likely to confess something of interest, compared to 51% without one.
So, in some situations, whether the tests work is beside the point. They are often used to simply scare examinees into confessing or answering truthfully during a pre-screen.
The idea of a polygraph may seem accurate, but overall, it only gets people to cooperate a large majority of the time.
Famous cases of inaccuracies
There have been many high-profile cases of guilty individuals passing polygraph tests.
In 1985, Mark Hoffman, who was later found guilty of the two murders he was questioned over, passed his lie detector test with exemplary results.
He was later convicted and told news outlets how he beat the exam, giving him more time to commit crimes. Hoffman admitted to practicing self-hypnosis to “split his personality” as well as using a blood pressure kit daily to control his reactions to questioning.
In another famous case, the Green River Killer, Gary Ridgway, passed a police polygraph test in which he stated he had no connection with the disappearance of some women local to the area. Ridgway would be dropped as a suspect, setting him free to kill 44 women until he was caught and convicted.
KGB spy Aldrich H. Ames, who was found culpable in the deaths of 48 CIA agents, passed two CIA lie detector tests with no issues. He later explained, “There’s no special magic.” “Confidence and a friendly relationship with the examiner…”
The Angel of Death, nurse Charles Cullen, murdered as many as 40 people by administering lethal injections. After his first victim died, Charles was asked to take a polygraph exam, which he passed. The failure of this exam resulted in the deaths of 39 more people.
Conversely, there have also been some high-profile cases of innocent people failing their lie detector tests.
When Vicki Wegerle disappeared in the 1980s, her husband failed both his police lie detector test and a privately hired expert polygraph test. In 2005, DNA evidence proved that Mrs. Wegerle was a victim of the BTK killer, Dennis Rader, a serial killer during the years 1974–1991.
In New York City, in 1988, an innocent man failed a polygraph exam during the murder investigation of Viola Manville. After Frank Sterling failed the exam, law enforcement coerced him to confess, and Sterling was sentenced to 22 years in prison for a crime he did not commit.
The killer, Mark Christie, who was also a suspect, passed his polygraph exam, giving him years to commit crimes such as abducting and murdering a four-year-old girl. When convicted of this crime, he confessed to the killing of Viola Manville, and Frank Sterling was released from prison.
In 2003, the National Academies of Sciences asserted that there is evidence that honest test subjects fall into “socially stigmatized groups.”
These are individuals who are already believed to be guilty because they may show emotional and physiological responses during an exam that could mimic the responses that are expected of a guilty person.
Accuracy of polygraph tests: our practical insights
There is an overwhelming amount of conflicting information regarding the accuracy of polygraph tests. Advocates such as the APA claim a close to 90% accuracy rate, while other studies claim much lower statistics, pointing out variables such as personality type, a person’s ability to deceive, how deception is measured, reaction to triggers, and an individual’s stress levels, guilty or innocent.
Using our actual experience as our basis, we have found that the lie detector’s accuracy is exceptionally high and typically ranges between 88% and 98% in real-world examinations, as opposed to study environments, with an average of 95% for each test taken.
Given the potential for a 5% margin of error on standardized exams, the majority of official organizations offer a second exam for test-takers who fail. Assuming that the two tests are independent (if the procedure is carried out properly, they should be as independent as possible), the probability of failing to detect deception in both tests would be:
0.05 x 0.05 = 0.0025 (or approximately 0.25% when rounded to two decimal places).
Hence, the probability that the polygraph would fail to detect deception in an individual after two independent tests is approximately 0.25%, indicating that, on average, approximately 99.75 percent of deceptive individuals would be identified as such by both examinations.
This indicates a high degree of precision. Though it is less than 100%, these rather high results show that the procedure is generally accurate.
The issue we have identified is that out of the 5% margin of error, the majority of the applicants that fail were truthful (false-positives) and comparatively less dishonest (false-negatives) ones. This is due to a number of reasons, including psychological, case-related, and procedure-related aspects.
Another concern is that in many cases, private sector polygraphers disregard these statistics and depend entirely on the findings of a single test.
It is important to mention that, typically, these are the upper and lower limits that vary based on the individual’s personality, the examiner, the case history, and the type of test.
What should you Do If your test is inaccurate?
If you have concerns regarding an inaccuracy of your personal polygraph examination, we offer individualized consulting services for wrongfully failed examinees.
Ultimately, your rights regarding polygraph test results vary depending on your country of origin and the instance of the test. Most countries, however, do not accept test results alone in criminal cases in courts or in pre-enrolment processes unless previously agreed upon. Either way, you may be able to retake a polygraph examination and, in some cases, appeal the results.
The accuracy of a polygraph test has been a subject of much debate and controversy. Some studies have shown that polygraph tests can be accurate up to 80-90% of the time, while others have suggested that the accuracy is much lower, around 50-60%. We have found the polygraphs accuracy to range between 88%-98% for each test taken. Factors such as the expertise of the examiner, the type of questions asked, and the subject’s physiological response can all impact the accuracy of the test.
There are several newer technologies that have been developed in recent years that claim to be more accurate than the polygraph. These include the functional magnetic resonance imaging (fMRI) test, which measures changes in blood flow in the brain, and the EyeDetect test, which uses eye-tracking technology to detect deception. However, these technologies are still in the early stages of development and have not yet been widely adopted.
Yes, it is possible to fail a polygraph test when telling the truth. This can happen if the subject is highly anxious or stressed during the test, which can lead to false positive results, although this occurs very infrequently.
As mentioned, There are several new technologies for lie detection that are being developed and tested, including the fMRI test, EyeDetect, and voice stress analysis. These technologies use different methods to detect deception, such as measuring changes in brain activity, eye movements, or vocal patterns.
The fMRI test has been proposed as a more accurate alternative to the polygraph, as it measures changes in blood flow in the brain rather than physiological responses to stress. However, Some experts have raised concerns about the cost and complexity of the fMRI test, as well as the potential for false positives and ethical issues related to brain imaging.
Help spread the word - share on social:
Former Israeli Special Forces officer, with over a decade of duty in vital national security roles.
Table of Contents
Might Also Interest You:
Legal Rights for Examinees in the U.S. (EPPA)
Read More »
Failed polygraph test
Read More »
Taking a Polygraph Exam? Ask These Crucial Questions First
Read More »
Are Online Polygraph Tests Legit? Getting To The Truth
Read More »
Read More »
Access the latest global intel:
Help spread the word - share on social:
Accelerating Solid Intelligence, From Every Corner of the Globe.
Axeligence is a privately owned provider of intelligence and investigations, comprised of veteran officersfrom elite Israeli intelligence units.