# Polygraph reliability **URL:** \ **Category:** Factual Questions\ **Created:** [March 31, 2017, 2:05pm UTC](https://boards.straightdope.com/t/polygraph-reliability/783411 "2017-03-31T14:05:38Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![SamuelA](https://avatars.discourse-cdn.com/v4/letter/s/c77e96/32.png) [@SamuelA](https://boards.straightdope.com/u/SamuelA)\ **Post date:** [March 31, 2017, 7:51pm UTC](https://boards.straightdope.com/t/polygraph-reliability/783411/21 "2017-03-31T19:51:41Z")
You know, when eyewitnesses are mistaken about what they saw - because each “recollection” of an event changes it as neural weights are adjusted - they aren’t lying. Even though they are not telling the truth. In principle, a truly expert liar could simply believe they are telling the truth and no test could discern any difference. Down to hypothetical “neural laces” that put electrodes on individual neurons. ---
**Author:** ![Bricker](https://avatars.discourse-cdn.com/v4/letter/b/977dab/32.png) [@Bricker](https://boards.straightdope.com/u/Bricker)\ **Post date:** [March 31, 2017, 7:52pm UTC](https://boards.straightdope.com/t/polygraph-reliability/783411/22 "2017-03-31T19:52:44Z")
> [@DrDeth](#): > > Cold reading is quite accurate, far more than a “blind guess”. However it should never- like the polygraph- be used in court. How about the court of public opinion? Prosecutor says, “I can’t comment on the record, but off the record after we arrested Smith, he failed the polygraph test, so we’re confident we’ve got the right guy.” Headline: ROBBERY SUSPECT FAILED POLYGRAPH, SOURCES SAY. ---
**Author:** ![DrDeth](https://avatars.discourse-cdn.com/v4/letter/d/b487fb/32.png) [@DrDeth](https://boards.straightdope.com/u/DrDeth)\ **Post date:** [March 31, 2017, 8:41pm UTC](https://boards.straightdope.com/t/polygraph-reliability/783411/23 "2017-03-31T20:41:31Z")
> [@Bricker](#): > > How about the court of public opinion? > > Prosecutor says, “I can’t comment on the record, but off the record after we arrested Smith, he failed the polygraph test, so we’re confident we’ve got the right guy.” > > Headline: ROBBERY SUSPECT FAILED POLYGRAPH, SOURCES SAY. Pretty bogus also, I’d say. It’s a valid investigative tool, to help narrow down suspects. But it is not evidence in any way. ---
**Author:** ![OldGuy](https://avatars.discourse-cdn.com/v4/letter/o/3bc359/32.png) [@OldGuy](https://boards.straightdope.com/u/OldGuy)\ **Post date:** [March 31, 2017, 8:52pm UTC](https://boards.straightdope.com/t/polygraph-reliability/783411/24 "2017-03-31T20:52:17Z")
> [@Marlonius](#): > > There was an incident in which, as a poorly thought out prank, someone put a sample of heavy water into the crew’s Gatorade cooler. Naturally, they were all setting off radiation alarms at detection points when they went to leave at shift change. Deuterium is not radioactive. Unless their heavy water was made with tritium, why would they set off radiation alarms? ---
**Author:** ![Czarcasm](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/czarcasm/32/4050_2.png) [@Czarcasm](https://boards.straightdope.com/u/Czarcasm)\ **Post date:** [March 31, 2017, 8:52pm UTC](https://boards.straightdope.com/t/polygraph-reliability/783411/25 "2017-03-31T20:52:24Z")
> [@DrDeth](#): > > It’s a valid investigative tool, to help narrow down suspects. But it is not evidence in any way. In what way is it a valid investigative tool? They don’t polygraph everybody-just the guy that they think is their main suspect. The polygraph “expert” already knows that she/he is the suspect and that the police would be pleased if he confirmed their suspicions…and he knows that someone else will be hired to do the job he is currently doing if he doesn’t give the police what they want to hear. It doesn’t take even a mediocre cold reader to do this. ---
**Author:** ![DrDeth](https://avatars.discourse-cdn.com/v4/letter/d/b487fb/32.png) [@DrDeth](https://boards.straightdope.com/u/DrDeth)\ **Post date:** [March 31, 2017, 8:58pm UTC](https://boards.straightdope.com/t/polygraph-reliability/783411/26 "2017-03-31T20:58:39Z")
> [@Czarcasm](#): > > In what way is it a valid investigative tool? They don’t polygraph everybody-just the guy that they think is their main suspect. The polygraph “expert” already knows that she/he is the suspect and that the police would be pleased if he confirmed their suspicions…and he knows that someone else will be hired to do the job he is currently doing if he doesn’t give the police what they want to hear. It doesn’t take even a mediocre cold reader to do this. Because he often confesses. ---
**Author:** ![Czarcasm](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/czarcasm/32/4050_2.png) [@Czarcasm](https://boards.straightdope.com/u/Czarcasm)\ **Post date:** [March 31, 2017, 9:02pm UTC](https://boards.straightdope.com/t/polygraph-reliability/783411/27 "2017-03-31T21:02:59Z")
> [@DrDeth](#): > > Because he often confesses. The police say you did it, the “expert” claims that he has evidence that you did it, the police put a “let’s get this done and close the book on it” deal on the table, and your public defender is ass-deep in clients that he hasn’t gotten to yet. Any amateur psychics want to predict the likely outcome of this situation? ---
**Author:** ![Just\_Asking\_Questions](https://avatars.discourse-cdn.com/v4/letter/j/ba9def/32.png) [@Just\_Asking\_Questions](https://boards.straightdope.com/u/Just_Asking_Questions)\ **Post date:** [March 31, 2017, 9:07pm UTC](https://boards.straightdope.com/t/polygraph-reliability/783411/28 "2017-03-31T21:07:23Z")
> [@Czarcasm](#): > > Change “knows” to “blindly guesses” and your statement is more accurate. It is fraud, plain and simple. No, my grammar was correct. The tester convinces the testee that he knows. I didn’t say he actually knew. He knows he doesn’t know. No one “knows” anything - that’s the beauty of it. (from a certain point of view) If your goal is to get confessions, it’s a useful tool. If your goal is to get accurate confessions, it is a slightly less useful tool. If your goal it to find the truth, it’s much less useful (I mean, people can still be fooled into telling the truth. It could happen.) If your goal is to determine who in your department is stealing, it’s nearly useles. If your goal is to root out the mole in your intelligence service, it’s negatively useful. ---
**Author:** ![Just\_Asking\_Questions](https://avatars.discourse-cdn.com/v4/letter/j/ba9def/32.png) [@Just\_Asking\_Questions](https://boards.straightdope.com/u/Just_Asking_Questions)\ **Post date:** [March 31, 2017, 9:11pm UTC](https://boards.straightdope.com/t/polygraph-reliability/783411/29 "2017-03-31T21:11:01Z")
> [@Czarcasm](#): > > The police say you did it, the “expert” claims that he has evidence that you did it, the police put a “let’s get this done and close the book on it” deal on the table, and your public defender is ass-deep in clients that he hasn’t gotten to yet. > Any amateur psychics want to predict the likely outcome of this situation? Sad but true. People will confess to stuff they didn’t do. I find it hard to believe people will confess to murders they did not commit, but it has happened. [After the shooting, four men from Tucson, referred to as the “Tucson Four”, were initially charged with the crime and gave confessions. However, they later recanted the confessions. Afterwards, all four were exonerated when it was discovered they had nothing to do with the crime](https://en.wikipedia.org/wiki/Waddell,_Arizona_Buddhist_temple_shooting) And that without a polygraph! eta: don’t overlook the fact that some people actually do confess to crimes they actually committed, actually. There are actual guilty people in prison. 🙂 ---
**Author:** ![Whack-a-Mole](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whack-a-mole/32/141_2.png) [@Whack-a-Mole](https://boards.straightdope.com/u/Whack-a-Mole)\ **Post date:** [March 31, 2017, 9:15pm UTC](https://boards.straightdope.com/t/polygraph-reliability/783411/30 "2017-03-31T21:15:04Z")
> [@DrDeth](#): > > Cold reading is quite accurate, far more than a “blind guess”. Do you have studies that back that up? Law enforcement types commonly claim to be able to spot liars but the data shows they can’t do better than chance in most cases (i.e. guessing if the person is lying). Now, there are certainly investigative and interviewing techniques that might be able to get a person to divulge information they want to keep secret and some interviewers can be quite adept but that is different from being able to spot a lie. > [@](#): > > Despite the popular appeal of body language, no study has uncovered any single behavior that accurately reflects whether a person is lying. It seems that for every study that finds an increase in a particular behavior—eye contact, illustrators, or gestures—another reports a decrease in the same activity. This is due at least in part to the fact that people’s responses vary based on the kind of lie, time to prepare, interviewer’s strategy, and liar’s level of confidence.[3] Any time an investigator misjudges an innocent subject’s behavior, there is the risk of a double injustice—an innocent person being subjected to the scrutiny of further investigation, while the actual offender remains free to commit additional crimes. > > \ > > It is likely that anyone who interviews criminals for a living will be lied to on a regular basis. In a study involving 509 people from a variety of career fields and agencies, only the U.S. Secret Service agents performed better than chance (50 percent).[6] A number of other studies have provided similar results.[7] > > SOURCE: [https://leb.fbi.gov/2014/june/the-truth-about-lying-what-investigators-need-to-know](https://leb.fbi.gov/2014/june/the-truth-about-lying-what-investigators-need-to-know) ---
**Author:** ![DrDeth](https://avatars.discourse-cdn.com/v4/letter/d/b487fb/32.png) [@DrDeth](https://boards.straightdope.com/u/DrDeth)\ **Post date:** [March 31, 2017, 9:28pm UTC](https://boards.straightdope.com/t/polygraph-reliability/783411/31 "2017-03-31T21:28:33Z")
> [@Czarcasm](#): > > The police say you did it, the “expert” claims that he has evidence that you did it, the police put a “let’s get this done and close the book on it” deal on the table, and your public defender is ass-deep in clients that he hasn’t gotten to yet. > Any amateur psychics want to predict the likely outcome of this situation? You seem to be debating the\* morality\* of the device as opposed to the \*usefulness. \*:dubious: \*\*The two are radically different things. \*\* Should the police be able to lie to suspects? Are “no-knock” warrants ethical? and so forth. ---
**Author:** ![Czarcasm](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/czarcasm/32/4050_2.png) [@Czarcasm](https://boards.straightdope.com/u/Czarcasm)\ **Post date:** [March 31, 2017, 9:32pm UTC](https://boards.straightdope.com/t/polygraph-reliability/783411/32 "2017-03-31T21:32:15Z")
> [@DrDeth](#): > > You seem to be debating the\* morality\* of the device as opposed to the \*usefulness. \*:dubious: > > \*\*The two are radically different things. \*\* > > Should the police be able to lie to suspects? > > Are “no-knock” warrants ethical? > > and so forth. If it’s “usefulness” is in it’s use as a fake evidence finder/police confidence booster then, yes, it is extremely useful. ---
**Author:** ![DrDeth](https://avatars.discourse-cdn.com/v4/letter/d/b487fb/32.png) [@DrDeth](https://boards.straightdope.com/u/DrDeth)\ **Post date:** [March 31, 2017, 9:38pm UTC](https://boards.straightdope.com/t/polygraph-reliability/783411/33 "2017-03-31T21:38:04Z")
> [@Whack-a-Mole](#): > > Do you have studies that back that up? > > Law enforcement types commonly claim to be able to spot liars but the data shows they can’t do better than chance in most cases (i.e. guessing if the person is lying). > > Now, there are certainly investigative and interviewing techniques that might be able to get a person to divulge information they want to keep secret and some interviewers can be quite adept but that is different from being able to spot a lie. “…no study has uncovered any _single_ behavior…” _“There are some signs that appear more frequently among liars than truth tellers… This is because no single behavior accurately predicts whether a person is lying. Therefore, rather than focusing on a single behavior, investigators initially should conduct a baseline assessment. They must ask open-ended questions to glean as much information as possible while watching for indicators of emotion, cognition, and control. After completing these steps, investigators may ask closed-ended questions intended to elicit specific responses.”_ A good cold reader does not assess any one single behavior. > **[Psychology Or 'Cold' Reading Explained - Psychologist World](https://www.psychologistworld.com/cognitive/cold-reading)** > > What is cold reading and what's the psychology behind it? ---
**Author:** ![DrDeth](https://avatars.discourse-cdn.com/v4/letter/d/b487fb/32.png) [@DrDeth](https://boards.straightdope.com/u/DrDeth)\ **Post date:** [March 31, 2017, 9:41pm UTC](https://boards.straightdope.com/t/polygraph-reliability/783411/34 "2017-03-31T21:41:43Z")
> [@Czarcasm](#): > > If it’s “usefulness” is in it’s use as a fake evidence finder/police confidence booster then, yes, it is extremely useful. You are turning a GQ into a GD, debating morality instead of usefulness. I _personally_ opine that all polygraph machines should be junked and no government agency allowed to spend a nickel on such procedures. But that’s morality. Having worked with other Feds for two decades, I can state they are \*useful. \* Write your Congresscritter. Get them to forbid any polygraph funding. Fine. ---
**Author:** ![Czarcasm](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/czarcasm/32/4050_2.png) [@Czarcasm](https://boards.straightdope.com/u/Czarcasm)\ **Post date:** [March 31, 2017, 9:44pm UTC](https://boards.straightdope.com/t/polygraph-reliability/783411/35 "2017-03-31T21:44:24Z")
Good cold readers work with a large crowd intsead of pre-picked individuals for a damn good reason-their methods are designed to work that way. They are next to useless in a “polygraph” situation, because you cannot “shotgun” questions to an individual, nor can you build up a rapport with slick patter. Again, this has nothing to do with “expert cold readers”. ---
**Author:** ![DrDeth](https://avatars.discourse-cdn.com/v4/letter/d/b487fb/32.png) [@DrDeth](https://boards.straightdope.com/u/DrDeth)\ **Post date:** [March 31, 2017, 9:53pm UTC](https://boards.straightdope.com/t/polygraph-reliability/783411/36 "2017-03-31T21:53:19Z")
> [@Czarcasm](#): > > Good cold readers work with a large crowd intsead of pre-picked individuals for a damn good reason-their methods are designed to work that way. They are next to useless in a “polygraph” situation, because you cannot “shotgun” questions to an individual, nor can you build up a rapport with slick patter. Again, this has nothing to do with “expert cold readers”. I love it when a amateur makes a statement that is so very wrong. > **[Cold reading and criminal interrogation - Cold Reading](https://www.magicalapparatus.com/cold-reading-7/cold-reading-and-criminal-interrogation.html)** > > I receive a lot of correspondence about cold reading from all over the world, and most of it is very interesting. On more than one occasion, police officers ---
**Author:** ![DrDeth](https://avatars.discourse-cdn.com/v4/letter/d/b487fb/32.png) [@DrDeth](https://boards.straightdope.com/u/DrDeth)\ **Post date:** [March 31, 2017, 10:55pm UTC](https://boards.straightdope.com/t/polygraph-reliability/783411/37 "2017-03-31T22:55:02Z")
That being said, yes, the "Psychic " version of cold reading differs quite a bit from what Polygraph experts use. And some might object to that term, but that’s what my FBI guys used. ---
**Author:** ![Exapno\_Mapcase](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/exapno_mapcase/32/1051_2.png) [@Exapno\_Mapcase](https://boards.straightdope.com/u/Exapno_Mapcase)\ **Post date:** [March 31, 2017, 11:40pm UTC](https://boards.straightdope.com/t/polygraph-reliability/783411/38 "2017-03-31T23:40:47Z")
> [@DrDeth](#): > > I love it when a amateur makes a statement that is so very wrong. > [Cold reading and criminal interrogation - Cold Reading](https://www.magicalapparatus.com/cold-reading-7/cold-reading-and-criminal-interrogation.html) That’s a guy selling his book! That’s worse than anecdotal evidence! Look, bottom line. Do you have any - any - real scientific, blind or double-blind experimentation that gives any credence to cold reading? ---
**Author:** ![Marlonius](https://avatars.discourse-cdn.com/v4/letter/m/838e76/32.png) [@Marlonius](https://boards.straightdope.com/u/Marlonius)\ **Post date:** [April 1, 2017, 1:15am UTC](https://boards.straightdope.com/t/polygraph-reliability/783411/39 "2017-04-01T01:15:40Z")
> [@OldGuy](#): > > Deuterium is not radioactive. Unless their heavy water was made with tritium, why would they set off radiation alarms? From Wikipedia: In 1990, assistant plant operator Daniel George Maston was charged after he took a sample of heavy water, contaminated with tritium, a radioactive isotope of hydrogen, from the moderator system and loaded it into a cafeteria drink dispenser.[13] Eight employees drank some of the contaminated water.[14] One individual who was engaged in heat stress work, requiring alternating work, rest, and re-hydration periods consumed significantly more than the others. The incident was discovered when employees began leaving bio-assay urine samples with elevated tritium levels, one with particularly unusually high levels. The quantities involved were well below levels which could induce heavy water toxicity, but several employees received elevated radiation doses from the tritium and activated chemicals in the water. It is believed that Maston intended the exposure to be a practical joke, whereby the affected employees would be required to give urine samples daily for an extended length of time.[15] Apparently not found from alarms at shift change, but from urine samples. I had a tour of that same plant when I was older and recalled the story when I myself went through physical detectors and had assumed this was how the spiked Gatorade was discovered. ---
**Author:** ![DrDeth](https://avatars.discourse-cdn.com/v4/letter/d/b487fb/32.png) [@DrDeth](https://boards.straightdope.com/u/DrDeth)\ **Post date:** [April 1, 2017, 1:18am UTC](https://boards.straightdope.com/t/polygraph-reliability/783411/40 "2017-04-01T01:18:00Z")
> [@Exapno\_Mapcase](#): > > That’s a guy selling his book! That’s worse than anecdotal evidence! > > Look, bottom line. Do you have any - any - real scientific, blind or double-blind experimentation that gives any credence to cold reading? Authors of books arent cites now??? Credence? Who said anything about credence? It’s a investigation technique. It is used. It works better than torture. [Previous page](https://boards.straightdope.com/t/polygraph-reliability/783411.md?page=1) [Next page](https://boards.straightdope.com/t/polygraph-reliability/783411.md?page=3)