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Why is it so hard to tell when people are lying?


Everyone lies at least once in a while. In fact, "once in a while" might be an understatement, a 2002 UMass study found that 60% of people will lie at least once during a 10-minute conversation if they're trying to appear likable. The vast majority of lies are so-called "white lies" — untruths about trivial matters, usually told to avoid hurt feelings and maintain smooth relationships. But bigger, more iniquitous lies are common too, and people naturally want to spot any lies they're told about more important matters. As a result, identifying lies has become a subject of both importance and popular fascination; there's even an annual lying contest in the UK, from which politicians and lawyers are barred on account of their professional-level skills.

Unfortunately, differentiating lies from truth by sheer observation is extremely difficult — more difficult than most believe, as it turns out. ClearerThinking recently conducted a study designed to gauge just how tough it is to identify lies through pure observation. Participants watched each other provide one true and one false answer to a question, and were asked to guess after each response whether the answer provided was truthful or dishonest. In total, the experiment involved 238 such guess-the-lie scenarios. The vast majority of participants predicted that they'd be able to correctly identify lies well over half the time; only a quarter of them predicted that they'd suss out falsehoods 50% of the time or less. In practice, though, the study group participants may as well have flipped a coin to determine which answer was true and which was false. Their accuracy rate hovered around 50%, and they were substantially overconfident to boot — their average degree of certainty in their guesses was about 60%. In fact, there was no correlation between the participants' confidence in each of their individual guesses and whether they were actually right whatsoever, suggesting that intuitive confidence may be particularly unreliable in lie detection.

This finding is especially remarkable because the study's format created a number of advantages that helped participants make their assessments. They knew that they were seeing lies half of the time; they were allowed to guess both after viewing each speaker's first answer as well as after the second answer; and they found out whether they were correct or incorrect after making their final guess about each speaker, thereby giving them a better sense of whether their lie detection methods had worked than is typically possible while trying to identify lies. Each participant enjoyed 15 instances of such potentially instructive feedback, to no avail. In spite of all these advantages, it turned out that the study group did no better at picking out falsehoods than random chance. (You can see a chart containing the data from the experiment at the bottom of this post if you're interested.)

Of course, this study — and most studies like it — couldn't capture the full complexity of high-stakes lie detection as practiced by the likes of police officers and other investigators, who often use the background facts of the situation and knowledge of the speaker's personality and motives to assess whether a statement is likely to be false. But identifying lies in real life also involves a broad array of complications and potential pitfalls that academic study participants don't face, many of which undermine the effectiveness of lie-detection techniques popular among those whose jobs require them to look for falsehoods.

Why is it so hard to tell when people are lying? An extensive systematic review of lie detection studies, compiled by psychologists based in England, Sweden, and Canada, attempts to answer that question. It identifies eight specific pitfalls that impede attempts to spot dishonesty through verbal and nonverbal cues:

  • No unique indicator of lying: Both lay people and professional lie-detectors — such as police manual authors — frequently believe that lies are reliably accompanied by giveaway hints, such as breaking eye contact, fidgeting, or speaking in a halting manner. Unfortunately, research into this question says otherwise. As the systematic review's authors put it: "The meta-analyses that have been published to date have made clear that there are no nonverbal and verbal cues uniquely related to deceit. In other words, reliable cues to deception akin to Pinocchio’s growing nose do not exist. The fact that there is no single cue that lie detectors can consistently rely upon makes lie detection inherently difficult...The meta-analyses further reveal that the majority of the nonverbal and verbal cues that researchers typically examine in deception studies are not related to deception at all."

  • Subtle differences between liars and truth-tellers: While liars do tend to reveal themselves with giveaways after a fashion, such as providing fewer details in their stories, the difference between liars and truth-tellers along these measures are quite minor, which makes them very difficult to identify informally.

  • Countermeasures: Liars who know they're being scrutinized may go out of their way to appear truthful. This might entail carefully rehearsing their stories, or attempting to project a truthful demeanor by suppressing the kinds of verbal and physical tics that others may associate (however incorrectly) with lies.

  • Embedded lies: Lies often come in the form of half-truths or selective omissions. In these cases, much of liar's speech really is true, deviating from reality only in an important detail or two. Such tactics make it difficult to differentiate lies from truth by means of verbal or nonverbal cues.

  • No adequate feedback: The only way to get better at detecting lies is to find out whether your lie-detection tactics are working, and that means learning whether your past assessments have been accurate. Unfortunately, this kind of feedback is relatively rare in real life — even police officials frequently don't learn conclusively whether suspected lies were actually false.

  • Violation of conversation rules: While it's possible to apply all sorts of pressure to people during interrogations in an effort to extract the truth, most lies are told in less frankly adversarial circumstances. A lot of the tactics available for pressuring people into revealing lies don't work in casual conversation because they're too confrontational — many people would simply break off a discussion when they realize they're being cross-examined.

  • Good liars: As noted by the British lying contest mentioned above, some people are just exceedingly effective liars. As the systematic review put it: "The best liars are those individuals (a) whose natural behavior disarms suspicion; (b) who do not find it cognitively difficult to lie; (c) who do not experience emotions such as fear, guilt, or delight when they are lying; (d) who are good actors and who display a seemingly honest demeanor; (e) whose attractiveness may lead to an inference of virtue and honesty; and/or (f) who are ‘good psychologists.’"

  • Lack of motivation to catch liars: In many situations, it simply doesn't occur to people that the statement in question might be a lie, thereby stopping efforts to pick out the lie before they start. Alternatively, people might have a specific motive to accept a potential lie as true. Many "white lies," such as insincere compliments, benefit from such motivated trust.

These challenges make lie detection a daunting prospect, and many of the common strategies to deal with them actually exacerbate the problem. Consider some common police interrogation tactics, for instance. Confronting suspects with the available evidence gives them an opportunity to alter their story to accommodate what the interrogator already knows; accusing them of lying provides them with an excuse to stop cooperating on the grounds that the interrogator won't believe them anyway; and looking for signs of nervousness in the suspect might mislead the interrogator, as truthful people can reasonably feel nervous about being the subject of a police investigation.

So how should we improve our ability to detect lies? The systematic review we've been discussing suggests some strategies that might be of use to police officials and other interrogators, such as increasing the cognitive load on interviewees by asking them to tell their stories backwards or requiring them to maintain direct eye contact throughout the interview. However, most of these tactics would be very difficult to deploy for normal people in casual conversation.

That being said, liars benefit when others are overconfident in their ability to detect lies. Being aware of how difficult it is to pick up on falsehoods in itself makes for a strong first line of defense.


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