How to spot a liar? Researchers evaluate what science knows

A toy representing Pinocchio's growing nose after a lie ©BelgaImage

This is a study that could give pause to the Belgian authorities, who have allowed the use of lie detectors (in other words, lie detectors) for 20 years. Posted 2 months ago Researchers from Sweden's University of Gothenburg are trying to piece together five years of work and meta-analyses on “indicators of deception.” In simpler terms, they pooled the conclusions of 50 experts to see if it was possible to spot liars. A synthesis intended to be comprehensive enough to claim to represent the scientific consensus on the topic. But at the risk of disappointing you, there are many prejudices and few real signs to know who is lying or not.

No, stress is not a reliable indicator

It is a common idea, for example, that liars are reluctant to meet another person's gaze. On this point, the study is conclusive: it is false! 82% of the experts agreed that there is no relationship between the two behaviors. Another fairly broad consensus: 70% of them agree that liars are no more stressed than honest people. A problem when we know that the lie detector depends on measuring pressure to make its judgements.

Sometimes the debate is more heated. There is no clear majority to say whether liars are more likely to move constantly, take a certain amount of time to respond, or express themselves more or less easily. For the Swedish researchers, these criteria cannot be used to identify reckless people.

Give details: Weak point of liars?

Let's put an end to the suspense: There's still a clue that could be helpful in figuring out how to detect it, according to about 72% of experts. The key will be to ask them for details. In other words, if a person can easily lie without being detected, it becomes complicated if they are asked to provide details. Because they have to invent more and more elements in order not to be detected, they tend to adopt disjointed, even incoherent, discourse. Right now, it will be the most effective tool to find out who is lying and who is not.

But the Swedish study was quick to point out that this hypothesis did not receive an approval rate of no less than 80% among experts. Therefore, its authenticity is still in doubt. For example, we can imagine that a person who is stressed, whether because of what he has experienced or because of an investigation, becomes confused in his memory. Conversely, the liar who predicted the event could have created an entire scenario around his lie.

Clues that vary from person to person

This difficulty has led Gutenberg researchers to suggest that it may actually be a stretch to design deceptive signals that would work every time for everyone. That's what the study's lead author, Timothy Locke, tends to tell BBC, identifying that each individual is unique and behaves differently. “Testing the same person under different conditions (known as a “repeated measures” experimental design) is the way to go“, explains his colleague Amina Mimoun.

This is what happened in the case of Donald Trump. In 2022, as part ofstudyThe researchers developed a language analysis tool to find out whether the former president's tweets were consistent with a desire to deceive or not. Result: The tool was able to achieve an accuracy rate of 74%. Therefore, language will be a distinct element in determining whether Donald Trump is lying or not, at least in part.

But it is clear that it is difficult for every individual to know what his weaknesses are. “The lack of consensus on key issues should be humbling for researchers trying to translate science into practice“, concludes the University of Gothenburg.”Disagreements among scientists mean we have a lot of work to do, and given the scale of disagreement, the work is unlikely to be boring“.