A quick review of the psychological research

by John M. Grohol, Psy.D.
February 2, 1999

I've been noticing that lately in the media, a lot of political commentators and politicians have been making outrageous scientific claims about their ability to tell when a person is lying. This has been brought up specifically regarding the need to depose witnesses live in the impeachment trial of President Clinton. Many laypeople, including many Senators and news media, apparently believe that people can make a pretty good assessment of when a person is lying or not. The research illustrates, however, that nothing could be further from the truth.

 University of Maryland professor, Patricia Wallace, in an upcoming book to be published later this year entitled, Psychology of the Internet, states, "Psychological research on deception [...] shows that most of us are poor judges of truthfulness, and this applies even to professionals such as police and customs inspectors whose jobs are supposed to include some expertise at lie detection." She then goes on to describe two of the many experiments in the psychological research literature which supports this contention.

 The first study was conducted in 1987 and looked at whether police officers could be trained to detect deceptive eye witness statements (Kohnken, 1987). They watched videotaped statements of witnesses, some of whom were truthful, others were not. They were told to pay close attention to non-verbal cues, such as body movements and posture, gestures, and facial expressions. They were also instructed to pay attention to the tempo and pitch of their voice. In the end, however, the officers did only slightly better than chance at determining whether the witnesses were being truthful. And the more confident the officer was of their judgment, the more likely they were to be wrong.

 Airline custom inspectors (whose very job is to try and determine suspiciousness and lying) and laypeople were used in another experiment (Kraut & Poe, 1980). The inspectors and laypeople in this experiment weren't given any specific training or instructions on what to look for. They were simply told to judge the truthfulness of mock inspection interviews viewed on videotape and determine whether the passenger was carrying contraband and lying about it. The "passengers" being interviewed were actually paid volunteers whose job it was to try and fool the inspectors. Neither laypeople nor inspectors did much better than chance. When questioned about what types of signs they looked for to determine lying behavior, the inspectors and laypeople relied largely on preconceived notions about liars in general: "liars will give short answers, volunteer extra information, show poor eye contact and nervous movements, and evade questions" (Wallace, in press).

 Wallace then goes on to explain that indeed, there are some people who can reliably detect deceit in others, and most successful poker players are usually such people. But most people are not professional, successful poker players.

 What nearly all deception experiments have in common to-date is that they use videotape instead of live people in their design. Some might argue that it is this very difference which politicians and others are trying to emphasize -- that people can't tell when people are lying on videotape, but can when the person is there, live, in front of them. Without research teasing out these subtle differences, however, it would be a leap of logic to simply assume that something is missing in a videotaped interview. This is a seemingly baseless assumption. A person interviewed on videotape is very much live to the people doing the interviewing. It is simply a recording of a live event. While there may be differences between the two, we simply don't know that any indeed exist. Without that knowledge, anyone who claims to know is simply speaking from ignorance or prejudice.

 The conclusions from this research are obvious -- trained professionals and untrained laypeople, in general, cannot tell when a person is lying. If you've known someone for years (a best friend, a family member, a significant other), your chances for detecting truthfulness is likely higher (since you have become accustomed to the signs of lying in the other person over the years). Strangers, however, trying to guess truthfulness in other strangers will do no better than chance in their accuracy.

 Psychological research has done a great deal of work in the area of understanding human behavior in the past few decades. The more people are aware that the research makes some of our most respected and well-known politicians and media stars look like fools, the more these individuals will hopefully do a little more homework before making future ridiculous claims about human behavior.

 The gulf between what we actually know and what we think we know is large. It likely grows larger each day. The more we realize the limits of our knowledge and our abilities, the wiser and more fair we can be to the people around us.


Kohnken, G. (1987). Training police officers to detect deceptive eye witness statements: Does it work? Social Behavior, 2, 1-17.

Kraut, R.E., & Poe, D. (1980). Behavioral roots of person perception: The deception judgments of customs inspectors and laymen. Journal of Personality and Social Psychology, 39, 784-798.

Wallace, P. (In press). Psychology of the Internet. New York: Cambridge University Press.

Last reviewed: By John M. Grohol, Psy.D. on 29 Mar 2015
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