# Why is lie detector technology not considered viable in a USA court of law? **URL:** \ **Category:** Factual Questions\ **Created:** [July 29, 2022, 8:11am UTC](https://boards.straightdope.com/t/why-is-lie-detector-technology-not-considered-viable-in-a-usa-court-of-law/968764 "2022-07-29T08:11:34Z")\ **Posts on this page:** 20\ **Page:** 5
**Author:** ![Riemann](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/riemann/32/3133_2.png) [@Riemann](https://boards.straightdope.com/u/Riemann)\ **Post date:** [July 31, 2022, 4:57am UTC](https://boards.straightdope.com/t/why-is-lie-detector-technology-not-considered-viable-in-a-usa-court-of-law/968764/81 "2022-07-31T04:57:57Z")
> [@Dr\_Paprika](#): > > both the sensitivity and sensitivity must be high > [@Monty](#): > > I think you forgot to change a word. That’s a Type O error. ---
**Author:** ![Dr\_Paprika](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr_paprika/32/3042_2.png) [@Dr\_Paprika](https://boards.straightdope.com/u/Dr_Paprika)\ **Post date:** [July 31, 2022, 5:17am UTC](https://boards.straightdope.com/t/why-is-lie-detector-technology-not-considered-viable-in-a-usa-court-of-law/968764/82 "2022-07-31T05:17:39Z")
No, I’m just oversensitive, specifically. ---
**Author:** ![md-2000](https://avatars.discourse-cdn.com/v4/letter/m/9d8465/32.png) [@md-2000](https://boards.straightdope.com/u/md-2000)\ **Post date:** [July 31, 2022, 5:47am UTC](https://boards.straightdope.com/t/why-is-lie-detector-technology-not-considered-viable-in-a-usa-court-of-law/968764/83 "2022-07-31T05:47:32Z")
> [@Monty](#): > > > [@Dr\_Paprika](#): > > > > both the sensitivity and sensitivity > > I think you forgot to change a word. That was my sense of the comment too. Also, speaking as a person (male) with a particular body type and BMI, the thing that makes you float or sink more than anything tends to be the subcutaneous layer thickness. I’ve tried snorkeling even with a 20lb weight belt and still float gracefully to the surface when I stop kicking. ---
**Author:** ![Cugel](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cugel/32/1199_2.png) [@Cugel](https://boards.straightdope.com/u/Cugel)\ **Post date:** [July 31, 2022, 7:57am UTC](https://boards.straightdope.com/t/why-is-lie-detector-technology-not-considered-viable-in-a-usa-court-of-law/968764/84 "2022-07-31T07:57:57Z")
I saw a TV program once that had a device that could tell (by measuring brain activity or such) whether a subject had seen an image before. So they could be shown an image of a crime scene, if the right lights came on, you are nicked sunshine. Doesn’t seem to have caught on. ---
**Author:** ![Schnitte](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/schnitte/32/9033_2.png) [@Schnitte](https://boards.straightdope.com/u/Schnitte)\ **Post date:** [July 31, 2022, 10:09am UTC](https://boards.straightdope.com/t/why-is-lie-detector-technology-not-considered-viable-in-a-usa-court-of-law/968764/85 "2022-07-31T10:09:27Z")
> [@SmartBulbInc](#): > > I mean, [52% of wrong convictions come from eyewitnesses](https://www.crf-usa.org/bill-of-rights-in-action/bria-13-3-c-how-reliable-are-eyewitnesses#:~:text=Researchers%20at%20Ohio%20State%20University,errors%20resulted%20from%20eyewitness%20mistakes.), yet they are still used as accurate in court. I’m not saying that lie detectors should be used as stand-alone evidence, but, 86% accuracy is still pretty high all things considered. There are two flaws in this post. The first is legal, in assuming that an 86 % accuracy rate (which I understand to mean that in 86 % of cases overall the lie detector arrives at the correct result, so that both a false positive and a false negative count as incorrect), if it exists, is somehow impressive. It is not. It means that the detector gets it wrong in 14 % of the cases, i.e., about one in seven. That’s _a lot_. In a system of the rule of law where you want guilt to be proved beyond a reasonable doubt before you convict, such an error rate is absolutely unacceptable. The second is statistical, in comparing the share of eyewitness testimony among wrong convictions to the accuracy of lie detectors. Even if your numbers are correct, the comparison between them is misleading, because they are calculated over very different baselines, as @kenobi_65 noted. Lastly, I’d like to note that judges and jurors are well used to the possibility that an eyewitness might be lying or misremembering things. They can take that into account when evaluating the strength of the testimony. With pseudoscience like polygraphs, the risk is that judges or jurors get impressed by technobabble and overrely on it to arrive at a false conviction. ---
**Author:** ![Dr\_Paprika](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr_paprika/32/3042_2.png) [@Dr\_Paprika](https://boards.straightdope.com/u/Dr_Paprika)\ **Post date:** [July 31, 2022, 3:12pm UTC](https://boards.straightdope.com/t/why-is-lie-detector-technology-not-considered-viable-in-a-usa-court-of-law/968764/86 "2022-07-31T15:12:13Z")
If it is true that lying involves certain specific areas of the brain, and I do not know if this is so - or reliable, then it may be possible, but not practical, to detect them. ---
**Author:** ![CookingWithGas](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cookingwithgas/32/485_2.png) [@CookingWithGas](https://boards.straightdope.com/u/CookingWithGas)\ **Post date:** [July 31, 2022, 4:19pm UTC](https://boards.straightdope.com/t/why-is-lie-detector-technology-not-considered-viable-in-a-usa-court-of-law/968764/87 "2022-07-31T16:19:00Z")
> [@Mama\_Zappa](#): > > > [@engineer\_comp\_geek](#): > > > > So, answer this. If you are innocent, would you be willing to face a lie detector that might have up to a 75 percent chance of wrongly convicting you? More than likely it’s going to convict you. > > I’d argue from a mathematical standpoint, that’s off. Assuming true negative = 75%, true guilty 85%, false guilty = 19%, and false innocent = 10%: You are convicted only if you get a false positive, or a true positive. It’s been too long since my last statistics class, so I can’t crunch the numbers reliably, but unless the people taking the test are largely in the group of guilty people, versus a random sampling, you won’t hit 75% bad outcomes. When looking at positive results from a person chosen at random from a population, you must also consider the base rate to be able to determine the chances this person is a true positive. However, if you’re the person and you know you’re innocent, the base rate doesn’t matter. ---
**Author:** ![DocCathode](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/doccathode/32/18773_2.png) [@DocCathode](https://boards.straightdope.com/u/DocCathode)\ **Post date:** [August 1, 2022, 1:06am UTC](https://boards.straightdope.com/t/why-is-lie-detector-technology-not-considered-viable-in-a-usa-court-of-law/968764/88 "2022-08-01T01:06:51Z")
I wish. I’m a couch potato who aspires to be a mad scientist. That’s all. I have no MD and no PhD. Though I do have ADHD. ---
**Author:** ![abcdefghij](https://avatars.discourse-cdn.com/v4/letter/a/43a26b/32.png) [@abcdefghij](https://boards.straightdope.com/u/abcdefghij)\ **Post date:** [August 1, 2022, 1:14am UTC](https://boards.straightdope.com/t/why-is-lie-detector-technology-not-considered-viable-in-a-usa-court-of-law/968764/89 "2022-08-01T01:14:06Z")
“They have one thing you haven’t got: a diploma. Therefore, by virtue of the authority vested in me by the Universitartus Committiartum E Pluribus Unum, I hereby confer upon you the honorary degree of ADHD.” ---
**Author:** ![Riemann](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/riemann/32/3133_2.png) [@Riemann](https://boards.straightdope.com/u/Riemann)\ **Post date:** [August 1, 2022, 1:24am UTC](https://boards.straightdope.com/t/why-is-lie-detector-technology-not-considered-viable-in-a-usa-court-of-law/968764/90 "2022-08-01T01:24:25Z")
> [@DocCathode](#): > > I have no MD and no PhD. Though I do have ADHD. > [@abcdefghij](#): > > …by virtue of the authority vested in me by the Universitartus Committiartum E Pluribus Unum, I hereby confer upon you the honorary degree of ADHD. And I think you now need to start saying “I have ADHD” with the same syllable emphasis as “I have a PhD”. ---
**Author:** ![DocCathode](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/doccathode/32/18773_2.png) [@DocCathode](https://boards.straightdope.com/u/DocCathode)\ **Post date:** [August 1, 2022, 1:34am UTC](https://boards.straightdope.com/t/why-is-lie-detector-technology-not-considered-viable-in-a-usa-court-of-law/968764/91 "2022-08-01T01:34:45Z")
But then folks would think I have a Dial Home Device for a Stargate. Come to think of it, I may do that. If I can say “I have a DHD” and they don’t think Stargate, do I really need to keep talking to them? ---
**Author:** ![dorvann](https://avatars.discourse-cdn.com/v4/letter/d/df705f/32.png) [@dorvann](https://boards.straightdope.com/u/dorvann)\ **Post date:** [August 1, 2022, 5:56am UTC](https://boards.straightdope.com/t/why-is-lie-detector-technology-not-considered-viable-in-a-usa-court-of-law/968764/92 "2022-08-01T05:56:59Z")
The interesting thing is the more people become aware how inaccurate polygraphs are the more inaccurate they will become because people will become less anxious taking them and it will harder to read that there are “lying”. ---
**Author:** ![Dr\_Paprika](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr_paprika/32/3042_2.png) [@Dr\_Paprika](https://boards.straightdope.com/u/Dr_Paprika)\ **Post date:** [August 2, 2022, 3:00am UTC](https://boards.straightdope.com/t/why-is-lie-detector-technology-not-considered-viable-in-a-usa-court-of-law/968764/93 "2022-08-02T03:00:56Z")
A lot of people have a pretty low degree of “awareness”. I think I first read about the crumminess of the tests forty years ago, and it was probably not breaking news then. It is already hard to read them since people express anxiety in different ways, and it probably depends on how it is administered and where; yet the test measures something different from what it purports to measure. ---
**Author:** ![eschereal](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eschereal/32/18939_2.png) [@eschereal](https://boards.straightdope.com/u/eschereal)\ **Post date:** [August 2, 2022, 8:11am UTC](https://boards.straightdope.com/t/why-is-lie-detector-technology-not-considered-viable-in-a-usa-court-of-law/968764/94 "2022-08-02T08:11:07Z")
Man, just use this thing [![](https://c1.staticflickr.com/9/8179/7963925830_4427333489_b.jpg) ](https://c1.staticflickr.com/9/8179/7963925830_4427333489_b.jpg) and be done with it. Even if you did not do it, it will still identify whether you have criminal tendencies and deserve to be punished. ---
**Author:** ![Elmer\_J.Fudd](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/elmer_j.fudd/32/1211_2.png) [@Elmer\_J.Fudd](https://boards.straightdope.com/u/Elmer_J.Fudd)\ **Post date:** [August 2, 2022, 2:17pm UTC](https://boards.straightdope.com/t/why-is-lie-detector-technology-not-considered-viable-in-a-usa-court-of-law/968764/95 "2022-08-02T14:17:07Z")
The best (yet still far from reliable) lie detector is a good interrogator. And that’s all a good polygraph operator really is. ---
**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:** [August 2, 2022, 5:29pm UTC](https://boards.straightdope.com/t/why-is-lie-detector-technology-not-considered-viable-in-a-usa-court-of-law/968764/96 "2022-08-02T17:29:04Z")
What ever happened to Voice Stress Analysis? That was going to be the Next Big Thing, the much more reliable detector than polygraph. It was supposed to actually work. This was like 45 years ago. Even then, as noted, “we” all knew polygraphs were unreliable. Yet people seem to still use them to this day. ---
**Author:** ![DrDeth](https://avatars.discourse-cdn.com/v4/letter/d/b487fb/32.png) [@DrDeth](https://boards.straightdope.com/u/DrDeth)\ **Post date:** [August 2, 2022, 5:34pm UTC](https://boards.straightdope.com/t/why-is-lie-detector-technology-not-considered-viable-in-a-usa-court-of-law/968764/97 "2022-08-02T17:34:26Z")
That is the critical tool- the interrogator, the polygraph is just a prop. > [@Just\_Asking\_Questions](#): > > What ever happened to Voice Stress Analysis? Indicates you are _stressed_, by your voice. Not that you are lying. ---
**Author:** ![k9bfriender](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/k9bfriender/32/3283_2.png) [@k9bfriender](https://boards.straightdope.com/u/k9bfriender)\ **Post date:** [August 2, 2022, 8:09pm UTC](https://boards.straightdope.com/t/why-is-lie-detector-technology-not-considered-viable-in-a-usa-court-of-law/968764/98 "2022-08-02T20:09:38Z")
> [@DrDeth](#): > > Indicates you are _stressed_, by your voice. Not that you are lying. Yeah, well why are you so stressed, if you’re not lying? ---
**Author:** ![md-2000](https://avatars.discourse-cdn.com/v4/letter/m/9d8465/32.png) [@md-2000](https://boards.straightdope.com/u/md-2000)\ **Post date:** [August 2, 2022, 8:12pm UTC](https://boards.straightdope.com/t/why-is-lie-detector-technology-not-considered-viable-in-a-usa-court-of-law/968764/99 "2022-08-02T20:12:09Z")
Because you’re being interrogated by a no-neck who is itching for an excuse to find you guilty? ---
**Author:** ![Great\_Antibob](https://avatars.discourse-cdn.com/v4/letter/g/e47c2d/32.png) [@Great\_Antibob](https://boards.straightdope.com/u/Great_Antibob)\ **Post date:** [August 2, 2022, 9:21pm UTC](https://boards.straightdope.com/t/why-is-lie-detector-technology-not-considered-viable-in-a-usa-court-of-law/968764/100 "2022-08-02T21:21:13Z")
Indeed so. My anecdote is getting polygraphed as part of a job interview. I was nervous about some pot smoke I might once have inhaled in college but the interviewer seemed a lot more concerned about potential foreign ties and kept coming back to that (I have no close family overseas and had only personally been to my parents’ homeland 2 or 3 times at that point and never for more than 2 weeks). I lost nearly all respect and trust in polygraphs after that. Seemed to me more about the interrogators’ preconceptions than anything else, which in that case seemed driven more by my ethnicity than any potential criminal activity. [Previous page](https://boards.straightdope.com/t/why-is-lie-detector-technology-not-considered-viable-in-a-usa-court-of-law/968764.md?page=4) [Next page](https://boards.straightdope.com/t/why-is-lie-detector-technology-not-considered-viable-in-a-usa-court-of-law/968764.md?page=6)