THE BLOG

What's the Most Accurate Lie Detector? It's Not What You Think

03/09/2015 04:40 pm ET | Updated May 07, 2015

The most well known contender, the polygraph, is an instrument that measures various physiological signals from sensors attached to a person undergoing questioning. The science behind the polygraph is based on the premise that under the stressful affect of questioning about potentially deceptive issues, a person will show changes in emotional arousal and cognitive load.

A sensor wrapped around the chest monitors respiration. Another on the upper arm checks blood pressure. Two sensors attached to the fingers monitor pulse and skin conductance (sweat). During questioning about issues related to a person's actions, there can be physiological reactions that indicate deception.

The polygraph was invented in 1921 by John Larson, a medical student at the University of California at Berkeley and a Berkeley police officer. ( Source.) Ironically, the original purpose of the instrument was to make police officers more law-abiding. (Source.)

In 1936, the FBI used the polygraph for the first time in a criminal case. (Source.) It was intended to help modernize criminal investigations. It has also been used over the years to screen job candidates for sensitive private or public security positions in federal organizations such as the CIA, FBI and NSA -- as well as for municipal police departments.

Today in the U.S., the polygraph is limited to government and law enforcement applications, as well as others where a person willingly agrees to be tested or in cases involving departments of corrections. In the U.S., the Employee Polygraph Protection Act (EPPA) of 1988 has limited the use of the polygraph used by private companies based on concerns about privacy and potential abuse.

Unfortunately, the polygraph does not necessarily measure concealed knowledge. And so from the beginning, concerns about the examiner's reliance on subjective interpretations to determine knowledge have been raised. Its accuracy has been strongly debated for more than 90 years. The issue is quite polarizing.

Under the right circumstances and with a skilled certified examiner, the polygraph can be very accurate at detecting deception; however, the best use case is for interrogations focused on single events such as a particular crime.

Polygraph accuracy depends on the skill of the examiner, the subject's physiology, and the conditions under which it is used--specifically if used for interrogation related to a particular event. If all conditions are prime, results can be fairly accurate.

In fact, under prime conditions, the American Polygraph Association says the accuracy of a polygraph can be over 90 percent. (Source.) Nevertheless, the challenge is that conditions are not always prime, examiners are not always skilled, and polygraphs are used for circumstances other than single event interrogations. Under those conditions, accuracy can be as accurate as a coin toss.

Some of the challenges with polygraph examinations include the following:

  • Prior to the test, a tense or strained interaction between the examiner and the subject can affect the outcome.
  • The examiner must rely on subjective interpretations of the measurements.
  • Some guilty individuals have successfully deceived the examiner by controlling their emotions with countermeasures such as biting the cheek or stepping on a tack inserted into the shoe.
  • Innocent people that react poorly to questioning have been labeled deceptive.
  • A polygraph test typically takes 2 to 3 hours and requires a skilled, certified examiner. If a person tires easily or is anxious, this amount of time may be excessive.
  • The test is somewhat invasive--sensors are attached to the fingers and chest--and some individuals feel anxious as a result.

In 1991, Drs. David Raskin and John Kircher of the University of Utah introduced the computerized polygraph primarily to mitigate concerns about subjective interpretation of data. (I spoke with Dr. Raskin.) In spite of that, the above-mentioned challenges are still in play.

Today, polygraph tests are not only used around for the world for criminal investigations but also to screen job applicants in all types of organizations. In fact, many more polygraph tests are given in some countries for pre-screening job candidates than for investigations.

But, if the polygraph is a better measurement of physiological changes and not concealed knowledge, is there a better solution?

In 2012, a significant study revealed that lying causes subtle changes in the behavior of the human eye because it induces a change in cognitive load. Fortunately, those changes are subconscious and cannot be masked by examinees under most circumstances. This method was shown to detect deception with 85 percent accuracy when used for generalized applications such as screening job candidates and employees. Those conditions are far more common than a criminal investigation.

The future of polygraph may soon change due to new innovations that prove to be more accurate and less invasive.

Note: This article and the opinions expressed here are from Russ Warner, VP of Marketing at Converus, makers of EyeDetect.