The cold hard facts: REAL figures of polygraph test accuracy (2023)

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.

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.

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