Humans have been trying to master lie detection for thousands of years — and failing miserably.
In fact, polygraphs aren't reliable. With as little as 15 minutes of training, people have been able to consistently beat the test.
The U.S. National Academy of Sciences has even said that "the Federal government should not rely on polygraph examinations for screening prospective or current employees, or to identify spies or other national security risks because the test results are too inaccurate."
So is there any way to detect lies based on real science? Actually, yes, and it involves understanding the psychology behind how liars think.
How to tell when someone is lying—and get the truth out of them
In 2009, the High-Value Detainee Interrogation Group, or HIG, was formed by the federal government to develop new lie detection best practices, and by 2016, the interagency group had spent more than $15 million on over 100 research projects with top psychologists.
So what do people who are incredibly good at catching liars on the spot do? I've adapted the HIG findings for simplicity's sake:
1. They are nice
You have to get the liar to like you. To open up. To talk a lot. And to make a mistake that reveals their deception.
A great trick is to think of yourself as a "friendly journalist." Good journalists do their homework before they write an article. The more information you have going into a conversation, the better calibrated your internal lie detector will be.
And then there's the "friendly" part. The HIG report found that "bad cop" isn't effective, but "good cop" is. Everybody wants to be treated with respect. And when people are, they're more likely to talk.
2. They don't rely on body language too much
Aldert Vrij, a psychology professor and leading expert on lie detection, says body language cues are rarely predictive.
Let me address a common myth directly: "Liars won't look you in the eyes." HIG's review of the research found that "gaze aversion has never been shown to be a reliable indicator."
And if that's not enough to dispel the myth, there's a 1978 study of the interpersonal behavior of incarcerated psychopaths. Guess what? They look people in the eyes more often than non-psychopaths.
3. They ask unanticipated questions
Ask an underage-looking person at a bar how old they are and you'll hear a confident "I'm 21." But what if you asked them, "What's your date of birth?" That's an exceedingly easy question for someone telling the truth, but a liar will likely have to pause to do some math. Gotcha.
The HIG report cites a study showing that standard airport security methods usually catch less than 5% of lying passengers. But when screeners used unanticipated questions, that number shot up to 66%.
So start off with expected questions. This is non-intimidating and gives you info — but more importantly, it gets you a baseline. Then, throw them a question that's easy for a truth teller to answer but that a liar would not be ready for.
Gauge the reaction. Did they calmly and quickly answer, or did their lag in answering suddenly increase?
Ask for verifiable details, too. "So if I give your boss a call, she can confirm that you were at that meeting yesterday?" Truth tellers will be able to quickly and easily answer that. Liars will be reluctant.
Another example: "What was Emily wearing at the meeting?" Again, easy for honest people, but a nightmare for liars. It's verifiable — and they know that.
4. They use strategic evidence
You did your homework in advance, right? Good. Build rapport. Get them talking. Lead them to say something that contradicts the info you dug up.
Ask for clarification so they commit to it. And then: "Sorry, I'm confused. You said you were with Gary yesterday. But Gary has been in France all week." Ask yourself the magic questions: Do they look like they're thinking hard? Does their hastily assembled reply contradict anything else, digging their grave deeper?
A 2006 study of Swedish police showed they typically detected lies 56.1% of the time. Those with "strategic use of evidence" training scored an 85.4%.
You want to incrementally reveal evidence. Repeated contradictions may get them to simply confess out of embarrassment. More likely it will make their lying increasingly obvious.
5. They don't challenge them too early
If you immediately start questioning what they say or accuse them of lying, not only might they shut down, but they also might start altering their story.
Why would you want to help them tell a better lie? The goal is to make them want to put it all out there and paint themselves into a corner.
Herein lies the problem in dealing with slippery people: They get good feedback, you don't. If I lie and don't get caught, I see what works. If I lie and get caught, I see what doesn't work.
On the other hand, the vast majority of the time you don't get feedback on whether someone was honest with you. So liars are always improving. You aren't. And that gives them an advantage. Don't help them improve further.
Eric Barker is the bestselling author of "Barking Up the Wrong Tree" and "Plays Well with Others: The Surprising Science Behind Why Everything You Know About Relationships Is (Mostly) Wrong." Eric has given talks at MIT, Yale, Google and the U.S. Military Central Command. Follow him on Twitter @bakadesuyo.
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*Adapted from "Plays Well With Others" by Eric Barker and reprinted with permission from HarperOne, an imprint of HarperCollins Publishers. Copyright 2022.