Though associated with relatively modern times, purported lie detectors have a long history. The ancient Chinese had suspects chew and spit out rice powder. If the powder was dry, the suspect was deemed a liar since it was believed fearful persons experienced a decrease in saliva. During the Inquisition, suspected liars were made to chew bread and cheese. If they choked due to a dry throat, this was considered proof of mendaciousness. Persons accused of witchcraft in Puritan America were submerged in water and, if they rose, considered liars. If they stayed submerged, they were shown to be honest and were vindicated, albeit victimized.

Polygraphs have as much use as rice and bread when it comes to weeding out lies. But they regularly appear in popular culture. And this, along with the graphs, needles, wires, and readouts, all overseen by men in white suits, give it an air of legitimacy.

Techniques vary, but the sessions usually begin with an examiner asking a subject general questions to establish a baseline. Then the serious questions are asked, with deviations from the baseline deemed to be lies.

Even the introductory questions can pose issues. The examiner may ask, “Have you ever cheated on a test?” Assuming most everyone has, a ‘no’ response will be seen as untruthful, even if it comes from a lifelong straight A student with no reason to ever do so. The examiner can then use that response as a baseline for determining deception, even though the response was honest. Also, if an examiner suspects a subject is untruthful, he could assume a more aggressive stance, making the subject more prone to a nervous response.

No science supports the idea of a correlation between physiological changes and lying. There are no studies suggesting examiners and their polygraph can detect lies at a significantly better rate than anyone else using a different method. There is no uniform physiological reaction to lying.

Furthermore, changes in heartbeat, respiration, and blood pressure can be caused by anger, embarrassment, fear, nervousness, sadness, or medical conditions. During one test of the polygraph’s efficacy, subjects were told, “I’m going to ask you an intimate and personal question.” This triggered the strongest reaction during the testing, even though no question was asked.

This highlights the polygraph’s biggest flaw: It cannot distinguish between deception and nervousness. An innocent person being grilled by police about a double murder won’t have all their mental and physical faculties. Since taking a polygraph test can make a subject nervous, it will be difficult for the baseline to be established. This will lead to inconclusive results, which can be interpreted as guilt.

Then there is the opposite issue, where a criminal like CIA spy Aldrich Ames can pass multiple polygraph exams. Likewise, most sociopaths will show no deviation from their baseline when being interrogated about a crime they committed.

Polygraph results are usually inadmissible in court and employers are generally proscribed from administering them. But governments are allowed to use them on their employees and this has led to ruined careers.

Counterintelligence officer Mark Mallah was considered deceptive when he denied ever having had unauthorized contact with foreign officials and was grilled for two days. Agents raided his home and placed him under 24-hour surveillance. It took 20 months for his full vindication to come. Mother Jones related the experience of Secret Service candidate Bill Roche, who had zipped through the year-long process until the final portion, the polygraph. The seven-hour session became increasingly belligerent, and Roche was accused of drug use, crimes, and workplace dishonesty. The hostile line of questioning made Roche more nervous, so the examiner labeled him deceptive and he lost any chance of being a federal law enforcement officer.

Despite incidents like this, governments continue to use polygraphs. Senator Richard Shelby led the drive to increase their use in the CIA, FBI, and Department of Energy. Shelby had his limits, however. He drew the line at extending its use to Richard Shelby. The FBI suspected he had leaked classified documents and wanted to test him, but he refused. And that’s the truth.