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Comment by jstummbillig | Hacker News Reader

I am so confused. There seems to be a blatantly obvious method to find out how well this machine works, no anecdotes or trust required: You get a decent amount of test subjects to dry run it in a controlled environment.

Has this not been done? If not, why? Or am I wrong in believing it's that simple?

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> Has this not been done?

No, this has not been done.

> If not, why?

Because it would fail.

> Or am I wrong in believing it's that simple?

Nope... it's that simple.

But let's be honest here: we SHOULD use this approach for ALL of these kinds of assessment, yet we don't. Even in the US, we use things like fingerprint matching, handwriting analysis, drug testing laboratories, DNA analysis, dog sniffs for drugs and so forth in legal cases yet we don't perform independent blinded tests of the accuracy of these tools.

Don't forget hair analysis.

And out of all of those, the only one that actually works is DNA analysis and even that fails from time to time due to how easily samples can be contaminated.

My understanding is that DNA is basically unique, but the patterns use for conventional DNA analysis are not. While they may be statistically close enough to unique to trust over the whole population, there have been different issues when you start scoping things to different racial groups or areas with smaller gene pools (not dangerously small, just smaller).

Because actually sequencing and comparing someones entire DNA would be prohibitively expensive if done for every case, they just look for a set of markers and assume that a large enough collection is close enough without accounting for distribution patterns of those markers AMONG THE SAMPLE POPULATION. (e.g. you don't have to look hard in small towns or in populations of the same heritage to notice a lot of physical characteristics that are quite common in that sub-population while being pretty distinct in the human population at large, the same is true for these markers.) . Since crimes often involve suspects from the same location and/or racial profile, a rule that is pretty reliable for the earth is not so reliable for this town/community/group of suspects.

So the science is a problem even before you get to human error. The odds of a false match take hits of multiple orders of magnitude.

Note: I'm not qualified to speak on the topic, but I've followed the topic with interest at a layman level for a while - be glad to hear from someone who IS qualified to speak on it to shed more light on why I'm right/wrong.

> My understanding is that DNA is basically unique

It is, in a lab environment with lots of source material.

If you are taking small samples of DNA from terribly dirty places and then amplifying the hell out of it, you get massive amounts of contamination.

Rape kits are "mostly" reliable under most circumstances, but have some problematic edge cases. Swabs from crime scenes, on the other hand, are generally garbage.

>My understanding is that DNA is basically unique, but the patterns use for conventional DNA analysis are not.

Even if they were, unless it's something like blood DNA after an attacker gets hurt, liquids from a rape, etc. it's trivial:

1) for the culprit to take another's DNA and place it on a crime scene

2) for an innocent to leave DNA at what would later be a crime scene

3) for police (or anyone with access) to add someone's DNA at a crime scene [1]

And the worst thing is, the DNA match then is considered "irrefutable" evidence...

[1] If you (3) is far-fetched, you haven't been following 100 years of police tampering to frame people, even in the USA, and much more in places like Latin America, etc. Just two recent examples:

https://www.buzzfeednews.com/article/melissasegura/detective...

https://www.huffpost.com/entry/baltimore-cop-drug-video-indi...

Where did you get the idea that print matching is untested...?

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3093498/

https://www.nist.gov/news-events/news/2004/07/nist-study-sho...

https://www.pnas.org/content/108/19/7733.short

The point is that the particular techniques used in court cases are often not verified by any scientific testing. The last sentence of the PNAS paper abstract is: "Examiners frequently differed on whether fingerprints were suitable for reaching a conclusion."

"Examiners frequently differed on whether fingerprints were suitable for reaching a conclusion."

is one of those weasel phrases which - while an accurate statement - means absolutely nothing because first "differing" in an opinion means almost nothing and the word "conclusion" is not defined.

Many people assert the Earth is flat and have detailed explanations on why that is the case, yet they "differ" in opinion too.

If fingerprints stood alone as a single point of evidence for guilty/innocent, I might agree. But it's used primarily as a "we have person A who matches close enough, let's go talk to him" that's useful. Or alternatively, if a fingerprint is one (of many) pieces of evidence that goes into making the case, that's useful. Only the worst cop shows say "the computer matched this guy! It must be him!"

* I was with the FBI on fingerprint analysis and saw the data, processes, etc and how a fingerprint is only a data point (aka clue) within the larger case.. and sometimes it's not enough depending on how many points you match.

It’s driven by two things - by the public perception that all bad guys fly coach (a la 911) and by governments seeking to expand the number of biometric means to enforce compliance of all sorts of things unrelated to travel. The irony is that many people who oppose a physical border wall on humanitarian grounds don’t seem to see the perils of virtual walls...such as when a visited country decides to share back my fingerprints it collected at the border with my home country despite legal protections against collecting my fingerprints when I’m inside/entering the home country OR any number of other applications that have nothing to do with border protection or everyday travel... unlike a physical barrier that can do nothing but it’s intended purpose. Sorry don’t mean to make this about borders but I’m trying to make a point that sometimes we use tech we end up creating entire new classes of problems worse than Ones we were trying to avoid... maybe the Amish have it right in this regard?

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?

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}.

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.

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.

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

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.

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

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

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!

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.)

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

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.

The purpose of these machines isn’t to actually work as intended. These machines are here for plausible deniability: “we pulled you aside because the machine said so, not because you’re Muslim”.

Or the computer said he was lying about not being a terrorist, so we went to arrest him but he was not cooperative and violently resisted, which of course is what a terrorist would do, and thus we had no choice but to shoot and kill him. In self defense of course and to protect the public. This is OK because the computer determined he was a terrorist and computers don't make mistakes.

Questions asked by the EU parliament:

http://www.europarl.europa.eu/doceo/document/E-8-2018-005624...

Answer:

http://www.europarl.europa.eu/doceo/document/E-8-2018-005624...

Apparently it has been tested, has been shown to have statistically significant result. As of November 2018 it was not used nor planned to be used on enforcing any border control, but was tested at three borders in real conditions.

Even a good system would have false positives. In itself, that does not invalidate the whole system, even if I think the whole premise of this project is very shaky.

Being statistically significant is nowhere near a high enough bar for this sort of quackery. Statistical significance is gameable, doesn't carry information about type I and II errors and frankly just means there is at least 1 common case that the machine gets right.

People shouldn't be given or denied opportunity because a magic machine likes them. This machine will be like a human - it will develop a bizarre set of biases and one of them will happen to be correlated with reality. It could be producing about as much evidence as someone guessing that Arabs are Muslim - grossly stupid, statistically significant results.

Honestly at 4.5m that's a marginal project that is unlikely to be used anywhere seriously. And the EU answers makes it clear it will never take decisions alone.

You know, there has been a bit weird push by brexit promoters for "frictionless" borders relying on magic tech. I suspect the funding of this could come from there.

Expect it to not go anywhere once the brexit mess is over

> Has this not been done? If not, why?

I'm no libertarian, but I will concede that this is a perfect example of libertarian griping about government spending: it's not getting done because no one has any incentive for it to get done.

Does the manufacturer have any incentive to honestly test the machine? Hell no, then no one would buy it.

Does the government have any incentive to honestly test the machine? No, because airport/customs security is security theater and their goal is convincing voters that "something is being done". (Voters might have an incentive to honestly test the machine, but it's more-or-less impossible for this preference to affect policy, unless huge numbers of people become single-issue voters about security device testing. Which isn't likely.)

Do the operators have any incentive to honestly test the machine? No, because if a terrorist slips through the machine and then blows up a plane, none of the blame comes back to the individual officer who ran the test.

Without any incentive for the machine to work, it's no surprise that it doesn't.

the point isn't detecting lies, the point is pressure to confess during interrogations. what matters is whether the person being interrogated thinks it works -- or even if they don't, to make lying more stressful.

Where are you finding terrorist who think they are getting away with concealing it?

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