The Polygraph and How to Cheat It - Interesting Engineering

Posted: 26 Apr 2019 12:00 AM PDT

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.

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.

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.

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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."

The Polygraph and How to Cheat It — *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.

How credible are lie detector tests? - BBC News

Posted: 04 Oct 2018 12:00 AM PDT

Image caption There are calls for Brett Kavanaugh to take a lie detector test as part of an investigation into alleged sexual misconduct

In a secure basement room of the US Capitol building, senators are reading a secretive FBI report into allegations of sexual misconduct made against Supreme Court nominee Brett Kavanaugh.

The contents of the report are not meant to be revealed, and there has been some criticism that the scope of the investigation has not been wide enough.

Throughout the investigation senior Democrats have called for Mr Kavanaugh to take a lie detector test. One of his accusers, Christine Blasey Ford, has already done so.

But how accurate are these tests? And how do they work? Let's start with the basics...

What is a polygraph test?

In short, polygraph tests record a number of different bodily responses which can then be used to determine whether someone is telling the truth.

They usually measure things like blood pressure, changes in a person's breathing, and sweating on the palms.

"The polygraph, like any other lie detection technique, measures an indirect effect of lying," says Dr Sophie van der Zee, who has expertise in forensic psychology and has researched deception for many years.

"There's no human equivalent of Pinocchio's nose," she says. "But lying can increase stress... and with lie detection techniques you can measure the behavioural and physiological changes that occur when you feel stress."

So polygraph tests do not measure deception or lying directly, but rather possible signs that a person could be deceiving the interviewer.

This information is then used in conjunction with everything else that is known about the person to form a clearer picture of whether or not they are being truthful.

How are they carried out?

Polygraphs have been used around the world, in countries such as Japan, Russia and China, but the technology remains largely the same.

"There's a fairly long pre-test interview that lasts for about an hour," says Prof Don Grubin, who has trained polygraph examiners in the UK. "This focuses the individual on the questions they're going to be asked and tries to remove any outside distractions."

This is followed by a practice test, which usually involves a number of straightforward questions. The aim is to relax the individual so they are comfortable and able to understand how the process works.

Image copyright Science Photo Library

Image caption Polygraphs measure blood pressure, changes in a person's breathing, and sweating

"There are no surprise questions because that in itself will trigger a response," Prof Grubin says. "What you're going to be asked is known."

The equipment is then attached, and it usually includes a blood pressure monitor, electrodes which are placed on the fingers or palm, and two tubes which are wrapped around the chest and stomach.

"There may be something that's put on the tip of the finger that records blood flow and we also use something called a movement detector which is on the seat and picks up if you're trying to beat the test," Prof Grubin explains.

"You'll probably be attached to the equipment for 10-15 minutes but you'll be in the room for about two hours," he says.

Interviewers ask a number of control questions during the test and then compare the responses to the key questions. It finishes with a post-test interview, where the person will be able to explain any responses they showed.

The curious history of the lie detector

Can you cheat?

Yes, according to the experts.

"There's no question that you can beat a polygraph test but you really need the training to do it," says Prof Grubin.

"You see websites telling you how to, but the reality is if you just go in and take a polygraph while hoping to beat it then you're not going to."

He says that it requires sitting down and practising with a trained examiner. But for those who don't have a qualified questioner to hand - what methods can work?

"You might put a tack in your shoe which will cause, for example, a big increase in your sweating response," Prof Grubin says. "Any sort of muscular activity or movement because you need to sit still."

"There are various drugs that people try but they tend not to be successful," he adds.

But he cautions that most examiners will be able to spot any covert attempt to beat the test.

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Media captionPolygraph tester Deepti Puranaik put the BBC's Rajini Vaidyanathan through a lie detector test

So do they work?

The credibility of the polygraph was challenged almost as soon as it was invented in 1921, and there is much debate about its accuracy.

Some experts say the fundamental premise is flawed.

"It does not measure deception, which is the core problem," says Prof Aldert Vrij, who has written extensively on the subject. "The idea is that liars will show increased arousal when answering the key questions, whereas truth tellers will not.

"But there is no sound theory to back this up."

Dr van der Zee says that, because taking a lie detector test can be a stressful experience, it can sometimes present innocent people as guilty.

"People being interviewed with a polygraph are likely to feel stressed. So whilst the polygraph is quite good at identifying lies, it is not very good at identifying truths," she says.

Image copyright Getty Images

Image caption Washington officials experimenting with an early polygraph in 1922

But Prof Grubin says there are a number of different reasons why a test may be inaccurate. These include the questions being poorly formulated and the interviewer misreading the results.

"If the examiner is well-trained, if the test is properly carried out, and if there's proper quality controls, the accuracy is estimated between 80%-90%," he says, adding that this is higher than the average person's ability to tell if someone is lying.

However, he says that interviewing victims presents a separate problem.

"Testing victims is a whole different ball game because of the nature of what they're being asked about, you would expect a lot of arousal anyway," he says.

This means a victim, especially one recounting a traumatic experience, may appear as if they are lying because they are in an emotional state.

Ultimately, experts say there are many caveats to polygraphs and a number of different factors which can lead to an inaccurate result.

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