In November 1985, when a pudgy, bespectacled young man named Mark Hofmann walked into the office of University of Utah professor Charles Honts, he appeared calm and relaxed. Hofmann was in Honts' office to take a polygraph examination.

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Hooked up to the "lie detector" machine, Hofmann was asked about his involvement in the grisly bombing murders of a young father named Steve Christensen, and a beloved grandmother named Kathy Sheets. Proclaiming his innocence, Hofmann passed the lie detector test with flying colors.

How accurate is a polygraph ?

The reality was that Hofmann was guilty of both murders, along with dozens of other crimes including the forging of hundreds of thousands of dollars worth of rare documents. Following his convictions for murder, Honts visited Hofmann in prison and asked him how he had beaten the polygraph machine.

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Hofmann, who was a stickler for detail, replied that anticipating just such a contingency, he had set up a blood pressure monitor in his home and had practiced with it until he could control his blood pressure at will. Hofmann also said that he practiced self-hypnosis, and had been able to hypnotize himself into believing he was innocent while taking the test.

Polygraph test procedures

A polygraph machine measures and records certain physiological characteristics, including blood pressure, pulse, respiration, and skin conductivity, while a person is asked and answers a series of questions.

The assumption is that deceptive answers cause a person's blood pressure to rise, the rates of their pulse and respirations to elevate, and their skin to become more conductive electrically through sweat.

The polygraph machine was invented in 1921 by John Augustus Larson, who was both a medical student at the University of California, Berkeley and a police officer. Larson's protege, Leonarde Keeler, added galvanic skin response to the machine in 1939, then sold the device to the U.S. Federal Bureau of Investigation (FBI).

A polygraph machine consists of two pneumographs which are rubber tubes filled with air. These are placed around a subject's chest and abdomen to measure respiration.

A blood pressure cuff similar to that used in a doctor's office is placed around the subject's upper arm. Two plates called galvanometers are placed on the subject's fingertips to measure sweat produced there. Today, the old analog polygraph machines shown in movies and on TV have been replaced by digital ones.

Polygraphs are used by the FBI, the National Security Agency (NSA), and the Central Intelligence Agency (CIA) in hiring decisions. The Las Angeles Police Department (LAPD) and the Virginia State Police also use the polygraph to screen new employees.

Pros and cons of the polygraph

However, in 2003, the U.S. National Academy of Sciences (NAS) issued a report entitled, "The Polygraph and Lie Detection" which found that when a polygraph is used as a screening tool, "Its accuracy in distinguishing actual or potential security violators from innocent test takers is insufficient to justify reliance on its use in employee security screening in federal agencies."

A report to the U.S. Congress by the Moynihan Commission on Government Secrecy, concluded that "... the polygraph is neither scientifically valid nor especially effective beyond its ability to generate admissions".

Can you fail a lie detector test if you are nervous?

In 1986, CIA officer and KGB mole Aldrich Ames was facing a polygraph examination.

He sought advice from his Soviet handler on how to beat the machine, and he received this simple advice: "Get a good night's sleep, and rest, and go into the test rested and relaxed. Be nice to the polygraph examiner, develop a rapport, and be cooperative and try to maintain your calm."

Spy Aldrich Ames, Source: Wikimedia Commons

Ames passed this test easily and passed another one in 1991. Ames said, "There's no special magic ... Confidence is what does it. Confidence and a friendly relationship with the examiner ... rapport, where you smile and you make him think that you like him".

Can you fail a polygraph when telling the truth?

The generally acknowledged tactics for beating a polygraph machine are to carefully control your breathing, and to artificially increase your heart rate during what is called the "control questions."

These are innocuous questions that are designed to set a baseline for responses.

By becoming, in essence upset, during these control questions, it makes the responses to real questions, and possibly lies, indistinguishable from the truth.

Another tactic proposed to beat a polygraph is for the test taker to repeatedly poke themselves with a sharp object hidden among their clothes or in their shoes.

This provokes background stress, masking lies from the truth.

Uses of the polygraph

In United States v. Scheffer (1998), the U.S. Supreme Court left it up to individual jurisdictions whether polygraph results could be admitted as evidence in court cases.

New Mexico is the only state in the U.S. that allows polygraph exam results to be admissible.

In the states of Massachusetts, Maryland, New Jersey, Oregon, Delaware, and Iowa, it is illegal for an employer to order a polygraph either as a condition of employment or if an employee has been suspected of wrongdoing.

The Employee Polygraph Protection Act of 1988 (EPPA) generally prevents employers from using lie detector tests, either for pre-employment screening or during the course of employment, with certain exemptions.

In Canada, with the 1987 decision of R v Béland, the Supreme Court of Canada rejected the use of polygraph results as evidence in court. In the Canadian province of Ontario, an employer may not use a polygraph.

In 2018, Wired Magazine reported that in the U.S., an estimated 2.5 million polygraph tests are given each year.

The majority are given to police officers, firemen, paramedics, and state troopers. The average cost of each test is over $700, making the polygraph business a $2 billion a year industry.