[function_seven]

To the extent they work at all, lie detectors only do so if the person telling the lie has a real reason to lie. Skin in the game, high stakes, and real harm if their deception is uncovered.

Having a controlled environment to test this is really hard. You can't just have someone say, "My mother is 35" when their mother is really 53. That's a silly lie, and can be told with the same level of calmness as the truth.

So how do you design an experiment with "real" liars (telling non-trivial lies), while knowing which participants are lying or not?

[cwkoss]

You let participants know that they'll receive money for every lie they "get away with" making them feel loss-aversion.

This has been used in psychological studies, but it's effectiveness is proportional to cost of doing the study, so it is expensive to get large datasets.

[WalterBright]

Lying to get away with $10 is a lot different from lying to get away with murder.

[Reelin]

If the machine could catch people lying for $10 (or $50, or ...) in a double blind study, that would set a quantifiable lower bound for its effectiveness.

[rasz]

1 How do you know. 2 Not for a psychopath.

[chaorace]

I have to disagree. A psychopath will value their freedom more than $10 and will be inclined to react differently.

[floatboth]

False positives are more concerning here than false negatives. It should be obvious to everyone that way way more people are "not calm" for reasons other than lying!

[function_seven]

Yeah. My "to the extent..." preamble represents my feeling on polygraphs and lie detectors in general.

The entire situation of being strapped into a machine and asked invasive questions is going to be nervous-making. And depending on which questions are asked, and how they're asked, the examiner can easily contaminate the exam and extract a false positive.

[sib]

That's an interesting point of view. If some hypothetical "bad guys" are trying to set off a series of tactical nuclear weapons, false negatives are actually pretty bad.

(Yes, I actually am a small-l libertarian and have a strong aversion to overbearing and stupidly-designed government programs, which this one certainly seems to be.)

[XorNot]

I mean if you have access to tactical nukes though, why are you even bothering to get on a plane in Europe?

[mos_basik]

Maybe you could induce something similar by providing the liar with strong incentives / stress. Something like this:

>We're going to hook you up to a state-of-the-art polygraph. We know you've heard that polygraphs are snake oil, but we think we've made a breakthrough on this one, which is why we're running this test. Answer truthfully to all questions except the five on this shortlist. For any of listed questions, you may choose to lie. If you tell one undetected lie, you get $5. For each additional undetected lie, your payoff is multiplied by 1.9. If any of your lies is detected, you get no money and you get shocked. The intensity of the shock has a similar exponential relationship with the number of lies you told.

If shocking volunteers doesn't get past the ethics committee, then maybe you start off the volunteers with a baseline payout of $50 or so and allow the payoff to both grow and decrease exponentially. The goal being that on that fifth lie, they're really on the edge, knowing that they could either make a lot of money or get {shocked,nothing}.

[itronitron]

how about this -> we are going to tell you how to defeat the polygraph, which is easy because it is actually mostly BS, and we will pay you $100K if you successfully deceive the polygraph when the examiner asks you if you have been told how to defeat the test.

Then tell the polygrapher that everyone will lie on that question so they should flag all responses as lies. Then everyone's results can be evaluated by another polygrapher to determine who was lying 'well', with no payout needed.