Polygraphs: The evidence

[drkitten]

I was under the impression that the polygraph didn't detect "lies" but, specifically, body functions. If someone's very nervous or very calm, doesn't that kinda defeat the whole thing ?

No. It doesn't respond directly to body functions, but to changes in body functions. So if you're very nervous at the start, but you get even more nervous when asked a question related to the incident in question, you will be flagged. If you're very nervous at the start, but are uniformly nervous throughout the interview, you will probably pass.

Now, you're right that someone with superhuman "nerves of steel" could almost certainly pass a polygraph by simply willing his body to display no signs of stress whatsoever. Such people appear to be relatively rare in the general population, as do the "nervous Nellies." As to whether or not you can be trained to become such a superman --- that was one of the issues that the NAS was concerned about.

 

[drkitten]

If you don't want to write for SkepticReport, what about Skeptic Magazine? Or present it at TAM?

What about JFS? Why is it worse to present the material in a specialist journal with higher readership and greater impact?

 

[drkitten]

Well--
In your example, you cannot even rule out people with smaller feet (or to a certain extent, larger feet) because a small foot can go inside a big shoe, and a bigger foot can be somehat squeezed into a smaller shoe. So you neefd more data.
In acourt of law, there will be other evidence--not just shoe size but sole pattern, my fingerprints on the window, i was seen in the area at about that time, nobody could support my contention as to my whereabouts, mud matching the location, pawnbroker saying I sold him the jewells,etc--all of which make the shoe size very insignificant. A polygraph would require the same level of proof--supporting evidence, and probable cause to direct an investigation.

Again, so why single polygraph testing out? As you point out, there are flaws with the DA's argument. Given that I specifically termed him "incompetent," I recognize that.

You seem to feel that the same defense attorney who would fight the footprint report tooth and nail would somehow roll over and play dead when presented with a polygraph report. Or perhaps you feel that someone would be more likely to be fired over a pollygraph report than over footprint report. In either case, I don't see why you attribute polygraph reports with these magical talisman-like credibility properties.

Any evidence can be misused, which is precisely why it is so important to know the actual value of the evidence....

 

[Belz...]

Any of the time? Be serious.

We know it's been correct at least three times, because it correctly identified Kari as telling the truth, and Tore and Grant as lying.

Besides, if it was incorrect ALL of the time I'd be easy to correct the situation, no ?

 

[Belz...]

No. It doesn't respond directly to body functions, but to changes in body functions. So if you're very nervous at the start, but you get even more nervous when asked a question related to the incident in question, you will be flagged. If you're very nervous at the start, but are uniformly nervous throughout the interview, you will probably pass.

Now, you're right that someone with superhuman "nerves of steel" could almost certainly pass a polygraph by simply willing his body to display no signs of stress whatsoever. Such people appear to be relatively rare in the general population, as do the "nervous Nellies." As to whether or not you can be trained to become such a superman --- that was one of the issues that the NAS was concerned about.

I was already aware of the "changes in body functions". I worded it badly. Thanks. That answers my question neatly.

 

[CFLarsen]

The first was a video, which I can't watch right now. I've read the second. Like DrK, I'm coming up on a barrier of time I want to invest. Please just answer me.

What is the issure here? What is being contested? Polygraphs only? Polygraph interviews? Abuse of authority?

See post #51.

You seem to have plenty of interest.

What about JFS? Why is it worse to present the material in a specialist journal with higher readership and greater impact?

It isn't a question of publishing your argument in other publications. It's a question of publishing it in skeptical publications.

You're a skeptic, right? You know that other skeptics disagree with you on this. You think that they should be swayed by the evidence you point to.

Why won't you argue your case in front of your skeptic peers?

 

[drkitten]

Why won't you argue your case in front of your skeptic peers?

Which part of "it does not appear to be a worthwhile investment of my time and trouble" did you miss the first time I posted it?

 

[CFLarsen]

No. It doesn't respond directly to body functions, but to changes in body functions. So if you're very nervous at the start, but you get even more nervous when asked a question related to the incident in question, you will be flagged. If you're very nervous at the start, but are uniformly nervous throughout the interview, you will probably pass.

Wrong.

A polygraph is an instrument that simultaneously records changes in physiological processes such as heartbeat, blood pressure, respiration and electrical resistance (galvanic skin response or GSR). The polygraph is used as a lie detector by police departments, the FBI, the CIA, federal and state governments, and numerous private agencies. The underlying theory of the polygraph is that when people lie they also get measurably nervous about lying. The heartbeat increases, blood pressure goes up, breathing rhythms change, perspiration increases, etc. A baseline for these physiological characteristics is established by asking the subject questions whose answers the investigator knows. Deviation from the baseline for truthfulness is taken as sign of lying.
Source

 

[drkitten]

Wrong.

You've now crossed the border from misrepresentation into outright lying.

Your quotation:

A polygraph is an instrument that simultaneously records changes in physiological processes such as heartbeat, blood pressure, respiration and electrical resistance (galvanic skin response or GSR). The polygraph is used as a lie detector by police departments, the FBI, the CIA, federal and state governments, and numerous private agencies. The underlying theory of the polygraph is that when people lie they also get measurably nervous about lying. The heartbeat increases, blood pressure goes up, breathing rhythms change, perspiration increases, etc. A baseline for these physiological characteristics is established by asking the subject questions whose answers the investigator knows. Deviation from the baseline for truthfulness is taken as sign of lying.

Note the italicized bit, which directly support what I said.

The instrument responds to "deviation from the baseline," i.e. to changes in body functions, not to body functions themselves.

A person with high signs of stress generally (e.g. "heartbeat, blood pressure, respiration and electrical resistance") will establish a high baseline. A person who is "uniformly nervous throughout the interview" will not vary from that baseline, and therefore will have no detectable "deviations." Absent such deviations, there are no signs of lying, and the individual will pass.

A person who is "very nervous at the start, but [who gets] even more nervous when asked a question related to the incident in question" will display the noted deviations, and be identified as lying.

I stand by what I wrote -- and list this as another reason on my part not to touch your nasty little vanity journal.

 

[Jimbo07]

See post #51.

This?

Please provide the scientific evidence that the error rate in polygraphs is close to zero.

For what purpose? How 'close' to zero? Why don't you think it's been done already? What would presenting at TAM resolve? Would anyone there really care (honest question, I haven't been)? etc.

This is what this thread is entirely about.

It's entirely about a statement that raises more questions than it answers?

You seem to have plenty of interest.

I do. I don't have time to read the secondary links of someone who won't tell me their own position. I will credit you with mine:

I've been to a couple ride-alongs/interviews. I have not been to a polygraph interview. I've been exposed to just enough to wonder if what people think they know about law enforcement and what they actually know are two different things. In fact, this can probably be generalized to any complex discipline which has evolved over time (biology? physics? ). This was all triggered by a personal connection of mine.

It isn't a question of publishing your argument in other publications. It's a question of publishing it in skeptical publications.

Wow. I've often wondered if popular skepticism is somehow removed from science...

 

[Cardelitre]

and as far as argumentum ad consequentiam goes--in this case I don't believeit is applicable. My argument is not a logical falacy, it is just an evaluation of human nature and greed. From my reading, and from what I know, people have lost jobs and had careers derailed --all from a single polygraph test.

Well, so what? Human nature and greed or people losing their jobs has no influence on the hypothesis that polygraphs can dicriminate lies from truth in a tested sample with an efficiency significantly better than pure chance (or not, for all I know).

 

[remirol]

I've seen a variant of it that could be called the "gambler's proof": where you ask someone to bet a very large amount of money about the truth/validity of a given issue. Generally, the attacker sets the amount so high such that he can be confident the opposing party either doesn't have that much money available, or won't be willing to risk it on something so (comparably) trivial. It also requires that the validity of the issue in question cannot be determined easily, such that neither party can be certain of the truth prior to accepting the bet.

(Example: "If you're so sure the Patriots will win the Super Bowl, you should be willing to bet your house on it. Let's bet your house against mine, OK?")

In some instances, it can be used effectively to demonstrate the depth of someone's conviction in their stated ideas, but has no bearing whatsoever on determining the validity of the ideas themselves. It is generally a tactic used to attempt to stop discussion of a topic and force a concession to the attacker's viewpoint.

The requests to write a paper and/or present at TAM in this thread are similar.

That is a preposterous idea.

I agree, the tactic is completely preposterous, as is the idea that someone who claims to be a skeptic would resort to a "shout down" approach like the one I described above. So stop using the tactic, and start discussing the issue like a rational adult.

For what it's worth, I agree with at least one premise of this discussion: I do not believe polygraphs are useful for determining whether a single individual is lying. Whether polygraphs are useful for determining whether some part of a _group_ of people are lying is a different claim altogether.

Second, this is not an attempt to stop a discussion, quite contrary: The thread is opened specifically to get the evidence out in the open, to a much bigger audience.

I do not believe you. I think you are deliberately attempting to push a scenario and standard of proof that involves far more risk and effort than this issue and discussion warrant, for the express purpose of forcing skeptigirl to concede your point of view here on this forum _OR_ decline to present -- at which point you will bring up the declination at every opportunity as "evidence" to support your side.

Argue the issue itself, (if you can). But please stop the blather about her presenting at TAM; it's completely irrelevant to the issue itself.

We are talking about skeptics claiming evidence that lie detectors works.

Your statement is vague. Please quote the claim made that you object to.

 

[CFLarsen]

You've now crossed the border from misrepresentation into outright lying.

Your quotation:



Note the italicized bit, which directly support what I said.

The instrument responds to "deviation from the baseline," i.e. to changes in body functions, not to body functions themselves.

A person with high signs of stress generally (e.g. "heartbeat, blood pressure, respiration and electrical resistance") will establish a high baseline. A person who is "uniformly nervous throughout the interview" will not vary from that baseline, and therefore will have no detectable "deviations." Absent such deviations, there are no signs of lying, and the individual will pass.

A person who is "very nervous at the start, but [who gets] even more nervous when asked a question related to the incident in question" will display the noted deviations, and be identified as lying.

I stand by what I wrote -- and list this as another reason on my part not to touch your nasty little vanity journal.

I'm not lying. You miss the point of such questions entirely. The "easy" questions are asked to put the subject at ease so a baseline can be established:

The Questioning Procedures

1. First, you are "put at ease" by the administrator, and he or she talks to you about all the questions you already answered on a questionnaire or in the pre-interview. They put you at ease and tell you that it is completely normal (because it is) for some things to “suddenly” pop in your head about things you might have forgotten to mention in the pre-questionnaire/interview.
How to cheat a polygraph test

I sincerely doubt that you have much knowledge about polygraphs at all.

This?

For what purpose? How 'close' to zero? Why don't you think it's been done already? What would presenting at TAM resolve? Would anyone there really care (honest question, I haven't been)? etc.

Because I have yet to see all that many skeptics agree with skeptigirl. I certainly haven't seen evidence that the polygraph is that accurate as she claims.

It's entirely about a statement that raises more questions than it answers?

If skeptigirl is right, skeptics are wrong. That's pretty important.

I do. I don't have time to read the secondary links of someone who won't tell me their own position.

If you won't read the links, you won't be convinced, that's for sure.

I will credit you with mine:

I've been to a couple ride-alongs/interviews. I have not been to a polygraph interview. I've been exposed to just enough to wonder if what people think they know about law enforcement and what they actually know are two different things. In fact, this can probably be generalized to any complex discipline which has evolved over time (biology? physics? ). This was all triggered by a personal connection of mine.

Thank you for that. It doesn't constitute scientific evidence, though.

Wow. I've often wondered if popular skepticism is somehow removed from science...

It isn't. But this subject has been discussed by skeptics as well, also in their publications, by the leading skeptics. It's an example of pseudoscience, which definitely is a subject skeptics are interested in.

 

[rwguinn]

I'm not lying. You miss the point of such questions entirely. The "easy" questions are asked to put the subject at ease so a baseline can be established:

yes, you are.
Either that, or you best stop trying to discuss things in the English language, because your comprehension is worse than a US educated 6th grader.Those two snips, dr kittens and your quotation said exactly the same thing.

I sincerely doubt that you have much knowledge about polygraphs at all.



Because I have yet to see all that many skeptics agree with skeptigirl. I certainly haven't seen evidence that the polygraph is that accurate as she claims.



If skeptigirl is right, skeptics are wrong. That's pretty important.



If you won't read the links, you won't be convinced, that's for sure.



Thank you for that. It doesn't constitute scientific evidence, though.



It isn't. But this subject has been discussed by skeptics as well, also in their publications, by the leading skeptics. It's an example of pseudoscience, which definitely is a subject skeptics are interested in.

After all that, I agree--You're not lying. You are either trying to justify an untennable position, or you cannot read and comprehend English--or you are doing the typical CFL troll, which would get anybody else suspended.

 

[Cardelitre]

It isn't. But this subject has been discussed by skeptics as well, also in their publications, by the leading skeptics. It's an example of pseudoscience, which definitely is a subject skeptics are interested in.

Just a little question, since I am not particularly familiar with the skeptic-specific litterature, have the leading skeptics (or anyone else) performed an experiment that demonstrated that the polygraphs are not better than chance in determining the proportion of liars in a sample population? Is this published somewhere, I would be curious to see what kind of test led them to this conclusion?

 

[LTC8K6]

Does a polygraph work if the examiner cannot see the subject?

 

[drkitten]

You miss the point of such questions entirely. The "easy" questions are asked to put the subject at ease so a baseline can be established:

More misrepresentation. Nowhere in the quoted paragraph is the phrase "easy questions" or "put the subject at ease." mentioned. What is mentioned is the necessity of establishing a baseline.

Wikihow isn't a very good source for "how to beat a polygraph," by the way. You'll notice that their advice is largely the same advice that Tore and Grant tried to use (and failed). I have no real problem dismissing it under the "don't take diet advice from fat people" rule. But even Wikihow says that you're lying.

If it was necessary to be put "at ease" in order to work, then truly nervous people couldn't be examined. But that's not what Wikihow says.

The polygraph takes your baseline, which is your base physiological response when you are nervous. Even if you were not nervous, the baseline measures that as well. It matters not where the baseline is on the graph. What matters, is how that base line changes as the questions are asked. So, even if you are nervous as a rabbit with the baseline, you still will likely show an anticipation/relief response when asked a question you have lied about, or are holding back information about.

I sincerely doubt that you have much knowledge about polygraphs at all.

Shrug. I've lectured on them, professionally. I've reviewed papers on them. I don't need to have that much knowledge to spot misstatements, errors, and misrepresentations.

 

[Jimbo07]

If you won't read the links, you won't be convinced, that's for sure.

Of what? An abstract is a guide for further reading. Give me an abstract. State a position. Anybody!

It doesn't constitute scientific evidence, though.

Of what? Scientific evidence of my personal motivation?

I'm sorry. I've followed both these threads and finally decided to come in and ask what the hubbub was about. I've stated why I would even bother reading a thread on this subject. I have a certain understanding, and am willing to admit to errors. However, I have no idea what the central contention is.

Is it: polygraphs are not 100% accurate? Polygraphs should never be used? Some have suggested that it's about the efficacy of individual vs. group testing.

Note to remirol: I'll actually disagree. With what I've posted regarding interview tactics, I'd have assumed that polygraph interviews were more effective in individual cases. It's neat to see the group thing...

 

[remirol]

Note to remirol: I'll actually disagree. With what I've posted regarding interview tactics, I'd have assumed that polygraph interviews were more effective in individual cases. It's neat to see the group thing...

In this case, I'd ask: is it that the polygraph is effective, or that the interviewer is skilled at 'breaking' naive people and inducing a confession?

Would that same (hypothetical) interviewer be capable of a similar success rate by simply using a machine that appeared to be a polygraph, but instead of actually reading the interviewee's physiological responses, had its needles "jump" every time the interviewer stepped on a button on the floor?

(Has anyone ever designed a test similar to the above?)

 

[LTC8K6]

We know it's been correct at least three times, because it correctly identified Kari as telling the truth, and Tore and Grant as lying.

What was correct? The machine or the operator?