Polygraphs Do Not Work… Why Do We Still Use Them?


I have taken three polygraphs with different agencies and the things they seem most concerned about are drug use and theft from a workplace. Just be honest with the interviewer before your hooked up and you'll be fine. Most agencies provide a list of automatic disqualifers and as long as you don't have any of those you'll be alright. Ernesto, I wouldn't worry about going to strip clubs or 2 beers a week. That is much better than most of the people(myself included) I work with! Good luck.

I just took a poly on Wednesday. We sat for a while and went through my background questionairre that I had filled out when I applied. We discussed stuff in my background (my only real transgression was marijuana use as a teenager). After I owed up to everything, they hooked me up.

The examiner did ask me questions repeatedly, but assured me ahead of time that it was not indicative of me doing poorly on a particular question, but was to provide him the opportunity to see how I reacted to the questions several times so he could get a better reading.

All in all, it wasn't a bad experience. I found it somewhat amusing that I had a "strong response" to questions about my name, and to two questions regarding stuff that I have never done. The stuff I was nervous about (which I was honest about) had no problem.

He did say I was difficult to read, and he would have to take some extra time to analyze my charts, so I should hear from him tomorrow

#1: What types of questions do they ask?

It depends on the department and the examiner. Like they said above, drugs and theft seem to be popular topics. Also, it may help to know how a polygraph works (the old ones anyway, I'm not sure if the new voice analyzers work like this also). The polygraph measures "truth" by a combination of physiological responses (breathing, pulse, skin response, etc.) to the questions they ask. Since it is human nature to feel "different" when lying to somebody (specially if you are hooked up to such a machine!), then those physiological responses are automatic, kind of like shivering to warm you up. Having said that, don't be surprised if the examiner asks you some embarrasing questions, such as "have you ever had sex with an animal" or "do you ever have erotic thoughts about other men?". These questions aren't meant to catch you in a lie, the answer doesn't really matter. These are questions that will invoke the physiological responses similar to a lie, no matter if you lie or not. Think of these as comparison questions. If you have the same response to the sex with an animal question as you do to the "have you ever smoked marijuana" question, then that may be an indicator of lying. I hope that helps you out, if you want more information on how the polygraph works, ask jeeves or google works wonders.

#2: How are the questions formatted?

Every polygraph I've ever seen or been involved in has been "yes" and "no" questions only. Before they hook you up, you will answer a series of questions with the examiner. They may have you fill out a piece of paper where the question say's.."Have you ever smoked marijuana? If so, describe how many times and how much below". Then later when they hook you up, they'll ask.."Other than what you put on the sheet, have you ever smoked marijuana?". Then at the end of the test the final question is usually.."Have you been untruthful on any of the questions on the paper or questions asked during the test?"

#3: Should you sweat the polygraph?

The easy answer is no. If you filled out your personal history truthfully and are truthful during the examination, chances are excellent that you'll pass. You WILL be nervous, everybody is, just hang in there and it'll be over before you know it.


The polygraph does what it was designed to due accurately 100% of the time. That is, measure physiologic responses. It is not a lie detector. There is no such thing. The science behind it requires the examiner to interpret your physiologic responses to his yes or no questions. So it is 100% accurate in that it measures your pulse rate and respirations. It is not 100% accurate in terms of detecting deception. That's where the examiner skill comes in, and as far as that goes, you either believe in the science or you don't. The science is not considered reliable enough to be admissible in court, but obviously govt. agencies rely upon the results for pre-employment screening, so you have to live with the process.

Even if you’ve never been arrested, it’s entirely possible that you’ve been subjected to a polygraph test. They are often used to clear people for certain types of jobs. When looking at U.S. government agencies, about 70,000 of those positions require future employees pass this lie detector test. On top of that, law enforcement agencies use polygraph tests all of the time, to the point that the deciding factor in some plea bargains has rested on results from a polygraph test.

Interestingly enough, polygraph tests don’t actually work, and we’ve known this for a long time.

Leonard Saxe, a psychologist from Brandeis University and someone who has performed a lot of research on polygraph machines, stated, “There is no unique physiological sign of deception. And, there’s no evidence whatsoever that the things the polygraph measures – heat rate, blood pressure, sweating, and breathing – are linked to whether you’re telling the truth or not.” Furthermore, the National Research Council concluded in a recent report that, Almost a century of research in scientific psychology and physiology provides little basis for the expectation that a polygraph test could have extremely high accuracy.” 

As early as 1983, Saxe created a report for Congress that eventually lead the branch of government to make it illegal for private employers to use polygraphs in their hiring process. In 1998, the Supreme Court made polygraphic evidence inadmissible in federal court, citing that “there is simply no consensus that polygraph evidence is reliable.”

In the end, polygraphs are nothing more than a pseudoscience, so why are they still being used?

How Does a Polygraph Work? What Does it Do?

lie-detector-chartThe polygraph made it’s first appearance in the early 20th century. The finalized version of the test was able to measure a person’s galvanic skin response, breathing, blood pressure, and pulse. Even then, the evidence to tell if someone was lying by measuring these physiological responses wasn’t very strong. Added to that, each of these three responses are controlled by different physiological systems, so they would need to be connected in a very intricate way.

The current method that interrogators use when conducting a polygraph test were developed in the 50s and 60s. It’s called the “Control Question Technique.” In a quick summary, an interrogator would start by asking control questions, easy questions for the suspect to answer that would establish a baseline for their anxiety. After that, the interrogator would ask different questions (including questions about the case) to stress the suspect out. After all of this is done, an analyst would look over the data from the interrogation and see if the suspect had a “more stressed out reaction” to the relevant questions. The rest is history.

The polygraph clearly measures something, because it does all sorts of cool things when you ask people questions. The test only measures a person’s level of anxiety. As Saxe pointed out, “All these physiological measures are simply associated with fear and anxiety. And people are anxious, sometimes, when they’re telling the truth, and they can be not anxious, sometimes, when they’re lying. The more practiced you are at lying, the less anxiety is associated with it.”

infographic polygraphSome controlled studies on polygraph machines have shown that polygraphs are able to distinguish a liar from a truther in some cases, but these tests also misidentified a shocking number of people telling the truth and labeled them as liars. The National Research Council was quick to point out that these tests are flawed because they are mock crimes, innocent people being accused of real crimes would probably feel much more anxiety than those in a controlled lab experiment. The list of cons for the use of this test go onand onand on.

Why Do We Use It?

The polygraph’s greatest weapon is the belief that it works. It’s a prop used by law enforcement and some employers. They are a deterrent and in some cases, somebody who believes you can tell when they are lying are more liable to tell the truth. Unfortunately, sometimes the prop is too good, because there are many people (both interrogators and bystanders alike) who believe the polygraph is accurate and actually works.


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