• The Truth about Polygraphs

    This post is part of a series of guest posts on GPS by the undergraduate and graduate students in my Science vs. Pseudoscience course. As part of their work for the course, each student had to demonstrate mastery of the skill of “Educating the Public about Pseudoscience.” To that end, each student has to prepare a 1,000ish word post on a particular pseudoscience topic, as well as run a booth on-campus to help reach people physically about the topic.


    The Truth about Polygraphs by Kelsie Witt

    Leonarde_Keeler_1937Polygraphs are more commonly known as lie detector tests.  They are used on television shows and movies unmasking the truth and assisting in putting away criminals.  In reality polygraphs are widely used in four different sectors: law enforcement agencies, the legal community, government agencies, and the private sector.  Some of the major uses of polygraphs today are for interviewing suspects, interviewing potential job candidates, and monitoring convicted sex offenders.  It all sounds glamorous… a machine that can tell when someone is lying and essentially do a detective’s job for them, right? Wrong.

    Polygraphs are not lie detectors but are only used as such.  Polygraph machines measure physiological changes in the body.  These changes include blood pressure, heart rate, galvanic skin response, and respiration.  Generally a polygraph exam will begin with questions that are neutral to obtain a baseline.  Essentially, if the difference between the physiological changes that occur when the baseline questions are answered and the physiological changes that occur when the target questions are answered are extreme enough the polygraph examiner would determine that individual to be lying.  This type of measurement results in an extremely high false positive rate (up to 50%!).  In essence this would be the same as someone flipping a coin every time an individual made a statement, heads for truth, tails for lies.  The false positive rate would be about the same in the coin toss as in polygraph examinations.

    Why are the results so often inaccurate?  Because these physiological changes do not only happen when someone is lying.  I’m sure you sweat at times other than when you are not telling the truth, like when you are uncomfortable, or you are extremely nervous. And would be more nerve wracking than taking a polygraph exam whether it is for a job interview or because you are being accused of a crime you may or may not have committed? There are a variety of things that can influence the results of a polygraph – nervousness, needing to use the restroom, pregnancy, drugs and alcohol, lack of sleep, blood pressure conditions, tight and restrictive clothing, sickness, having a headache, and many more! So how do you know that there is not something happening, besides your answers, that is causing the machine to give false positives? You don’t…and neither does the polygraph examiner.

    As mentioned previously, it is plausible that a polygraph exam could be used during a job interview, especially if that interview is for a law enforcement agency.  Polygraphs are not typically used for employment outside of law enforcement because of the Employee Polygraph Protection Act (EPPA).  This prohibits business from not hiring an individual due to a polygraph alone or firing someone on the basis of a polygraph alone.  It is important to note that the EPPA does NOT apply to government workers, which is why a polygraph exam is often used for law enforcement job interview purposes, and can be the reason why someone does not receive that job.

    When it comes to using polygraph exams in court things are even less clear and defined. Some states, such as California, Arizona, Georgia, Nevada, and Florida, allow polygraph exams to be admitted as evidence in court as long as all parties agree to it. Florida even requires some previously convicted sex offenders to submit to polygraph exams but, because of their unreliability, these results are not used in court but for counseling purposes. Other states, such as New York, Texas, Illinois, Pennsylvania, and the District of Columbia, prohibit the use of polygraph exams as evidence in court.  A few of these will allow them to be used in gaining probable cause for search warrants but New York and Texas go so far as completely banning them from law enforcement.

    Federal courts allow judges discretion in their own court room as to whether or not they will allow polygraph exams but President George H.W. Bush banned polygraphs from military trials due to their unreliability.  Before 1993, polygraph exams were inadmissible in all courts according to Frye v. United States.  In this case, tests like the polygraph exam had not gained enough scientific evidence to be consider credible in court.  When the Daubert Standard came into effect in 1993, polygraphs started to become more widely used because it was no longer based on scientific evidence but on two core elements – whether it is relevant and reliable. Rather than being determined by weight of empirical evidence, these are determined by the judge. The error with allowing judges to determine the credibility of polygraph exams is that they do not often have any scientific background or knowledge and, even if they do, they do not necessarily have any background knowledge about polygraph exams themselves. How can someone that has no knowledge of a scientific, or in this case, a pseudoscientific technique make and educated decision about whether the technique should be admissible in court?

    The results of polygraph exams are first and foremost a pseudoscience. They are not allowed in all courts because there is no evidence that what they do is any better than chance. There is a law that prevents employers from using them against employees or potential employees because there is no evidence that what they do is any better than chance.  Polygraph examinations in no way pass scientific muster and cannot begin to pass through the scientific method.

    Category: PseudoscienceScienceSkepticismTeaching


    Article by: Caleb Lack

    Caleb Lack is the author of "Great Plains Skeptic" on SIN, as well as a clinical psychologist, professor, and researcher. His website contains many more exciting details, visit it at www.caleblack.com
    • Kaitie McElroy

      I think its amazing that polygraph test are used at all anymore in any field because of their pseudoscientific nature! It good to know that in many courts the polygraph is not allowed but its disheartening to find out though that they are allowed in some courts based on a judges belief in the validity of their results as it pertains to a particular case!

    • CatherineD

      It’s incredible that they didn’t start questioning the reliability of the polygraph for so long. I wrote my capstone over Hugo Munsterberg and he assisted in the developing concept of a “lie detector” back in the late 1800s. Really interesting read, good job Kelsie!

    • Kiersten Durning

      One of my biggest problems with polygraph exams is how much it is used and depended on for sex offender treatment. Sure the fear of the machine itself will probably make someone less likely to lie, but if the individual does not “pass” the exam they will not processed any further in their treatment. They then must repeat whatever stage they were in until they pass the polygraph. They base their whole treatment off these exams, and that’s what I find so ridiculous.

      • Kels

        I found that very astounding also. They do not find it reliable enough to sentence people but will make them continue in treatment for years and not allow them to move on because of it. It many aspects it is very much a double standard.

        • SStice28

          I also find it ridiculous that they use it for sex offender treatment. It seems to me that the criminal justice system needs to take more psychology and biology courses. It also saddens me that so much pseudoscientific nonsense has leaked into the criminal justice system. We need a total overhaul.

    • jordannpyle

      It simply astounds me that we even have use for polygraphs anymore. I can see how it was meant for good and how it was beneficial back in the day but I just feel that they are pointless now. We can see how inaccurate they can be, like you said, up to 50% of the time. Of course, I am extremely thankful they are not allowed in courts but they fact that they use this as a tool to provoke a confession from suspects disgusts me. The the fact that we know that they aren’t reliable and still allow the police and other organizations use them is repulsive. Sorry for my rant, this was very informative and I enjoyed it a lot!

      • SStice28

        I am glad that its not accepted as evidence either. Honestly, the results of these exams are subjective at best, and they can only indicate if someone is a good liar, or is under immense stress or not. Plus, they should really consider certain psychological conditions (e.g. antisocial personality disorder, schizophrenia, anxiety disorders, bipolar I & II) that can alter the results.

      • kellyjent

        Speaking about using it as a tool to provoke a confession from suspects makes me wonder if there is any relation or research done with polygraphs and false confessions. We know that certain interviewing techniques are likely to influence false confessions – but I wonder about the impact of adding polygraph results to that.

    • kellyjent

      Oh boy, this is going to be long. Okay, so in regards to the EPPA – it’s great to know that
      you aren’t allowed to not hire/fire someone solely based on polygraph results; however, I would imagine that once a test has been administered it’s hard to ignore the results – even if you’re good intentioned. For example, when a jury receives information in court that is then withdrawn and they are instructed to forget it – they don’t actually forget it…. it’s like the white elephant (white? purple? I don’t remember the color) example – if you’re being told not
      to think about a white elephant, you’re going to think about it and it’s probably going to influence your decision. Or, is the EPPA saying that they aren’t allowed to test employees at all?

      It’s also interesting that the results can be used for law enforcement jobs when polygraph results aren’t admissible in most courts…. what? If the court doesn’t recognize this as being a valid measure, why would you use it in law enforcement fields (out of all fields) for interviews?

      Also, unless I’m totally misunderstanding this, I like how the requirement for Daubert’s relevant claim is: whether or not the expert’s evidence “fits” the facts of the case. You can absolutely make these results appear relevant to your case. Reliability point (2) states: the known or potential rate of error associated with the method. If this is at all speaking to the 50% chance of the polygraph being wrong… I don’t see at all how it would pass. The last subset states that it must be generally accepted in the scientific community…. this
      is really frustrating.

      I also think that polygraphs have been used in the media (movies, etc.) often enough that to a lot of people it appears more valid than it is. Like, “Someone failed the polygraph test?!? They must be hiding something!!” I might be exaggerating a little, but for the courts that do
      allow these results it’s worrisome about how the jury will respond when they receive this information. That would be interesting as well – to see how much weight a jury gives to polygraph results in court. Looks like I have some research to do!

      Alright, I’m done for now. Great post though! I really enjoyed it. It’s especially interesting being in the field of forensic psychology – and I’m sure you were just as intrigued researching this.

      • Kels

        They actually can’t require them to take one at all. There are some special circumstances like in pharmaceutical manufactures that I didn’t really go into but you can read about it here: http://www.dol.gov/whd/polygraph/

        As far as the Daubert thing, I found that very fishy as well. It’s not better than 50% but it was still good enough to pass Daubert standards? I’m assuming the evidence was better when first establishing the polygraph if there was any. Because today polygraphs would most definitely fail the Daubert standard.

    • Kylerdean

      I had never heard of employers using polygraphs for potential job hires until now. It’s crazy to think that there are companies that actually base whether you land a job or not on whether you pass a polygraph. What makes it even more scary is that there are so many uncontrollable factors that can cause false outcomes which can land you behind bars or keep you on your job hunt. It sounds like it has become aware that these polygraphs are not reliable and good news that since they are so muddled they do not have much backing in court rooms now a days.


      Just a couple of weeks ago we had a guest speaker in Dr. Adam’s Intro to Forensic Science class from the OSBI who came to talk to us about jobs in forensic science. He’d mentioned that polygraphs were used in the hiring process. When I challenged him to support that practice, given the known and thoroughly documented inaccuracy of the device, all he could say was “well actually they are very accurate”, to which I replied “actually they are not, and there are decades-worth of research to prove it.” He really needs to read your post.

      • Ha, I love it! Call them out on the bullshit, Lisa 🙂

        • XxLR_JORDANxX

          I wanted to really get into it with the guy, but I have too much respect for Dr. Adams to seriously embarrass one of his guests, so I just let it go.

    • OklahomaTrey

      It’s sad it see how much a job application can be affected due to the polygraph. Last week, we had Commissioner of the Oklahoma Department of Public Safety speak in my class. It was unsettling that polygraph tests lasting up to four hours can be used. While this provides no evidence for any lying, but rather used as an intimidation technique tactics to infer if someone is lying. These have even affected family members as polygraphs have been implemented and used against job promotions and opportunities. This is a shame in a modern day where more scientifically validated methods could be used.

    • Amanda Beck

      Wonderful post. It makes me wonder if an individual committed a crime, but were perhaps in a psychotic state or suffering from a mental break, they may have limited recollection of what actually happened. This would allow the person to potentially pass a polygraph test, even though they actually committed the crime, simply because as far as they are aware, they didn’t actually commit the crime. You know, assuming people can actually commit crimes without knowledge. But if they believe they are innocent, it may appear as such on the test.

    • Scott Sims

      It is crazy how inaccurate these can be, and yet they are still used to determine some peoples fate. I recently saw something on the always reputable Maury show where they used a polygraph, and that was the first thing I thought of. Though I guess Maury has more problems than just the use of the polygraph.

    • Tammy

      Does anybody know if there is a link to failing a voice stress test and autism like if someone with autism could fail one even tho they were telling the truth