What is a Polygraph Test and Why it is NOT Accurate

Are Polygraph Tests Accurate?
No. Polygraph tests are not 100% accurate. Sometimes they work, sometimes they go askew! So when do they work? When do they fail to work properly? Why do they fail to work out? Find all your answers here.
To cut a long story short, no, polygraph tests are not accurate. Better known as a lie detector, a polygraph device is something that is supposed to aid the examiner to find out if a person taking the polygraph test is lying or not. It is tempting to want to believe that a polygraph device can accurately detect a liar, for each one of us, at some point of time, has wished to be able to tell if someone is lying or not. However, it has become a long-established fact now that not only are polygraph tests not accurate, they are heavily biased as well. To understand why polygraph tests are not accurate, let us first take a look at how the test is conducted.
Polygraph Test Procedure
Two people talking
First the person who is going to conduct the test will ask you some basic questions to gain background information about you (for example your full name, the name of your pet dog, the school you went to, etc.); sometimes a person undergoing the test is even asked to answer these questions in the form of a written questionnaire. Then the tester will conduct a mock test, where you will be asked to deliberately lie and give false answers. The tester will then detect these 'false' answers and hence prove the accuracy of the polygraph device to you. Finally, he will conduct the actual test. Here, the questions asked will be of three types; irrelevant questions (for example, "Is your dog's name really Rex?"), probable-lie questions (for example, "Did you ever cheat on your partner?"), and relevant questions (that is, questions actually related to what you are being interrogated about). The test is repeated several times, changing the sequence of the questions. Answers are recorded, the tester looks into the device, and you are caught if you are lying!
How the Polygraph Test Works
Worker tested by polygraph
Polygraph - the name makes you think it might be something on the lines of rocket science. But a polygraph test works in a pretty simple way. The variables measured by a polygraph include blood pressure, skin conductance, pulse and respiration. The logic behind a polygraph test is that: it is assumed that when people lie, they sweat, their heart races, their pulse shoots, their respiration becomes strained and heavy, their blood pressure drops, and their voices quiver. These are the very signs that the polygraph device looks for, or measures.
Why is the Polygraph Test NOT Accurate
Polygraph Test
There are several reasons why the polygraph test is NOT accurate. Topmost among these reasons is the reason that the test assumes that people exhibit the above mentioned symptoms when they lie. It could be possible that a person who is lying does not exhibit all or some of the above symptoms. How then would you know if he/she was lying or not?

The National Academy of Sciences (NAS) dismissed the reliability of polygraph testing as early as in 2003. According to investigations carried out by the NAS, the whole procedure is highly "Unreliable, Unscientific and Biased". Even if a polygraph device was detected to be 80% accurate, this would still be futile anyway, as the NAS extrapolated and demonstrated. Take for example the case of a polygraph device that has a success rate of 90%; i.e. out of 100 tests conducted on the device, 90 tests will be genuine and will help catch a liar. Hence, in the remaining 10 tests, innocent people will be pronounced liars! (These are called 'false positive results' or simply 'false positives'.) What if this test happens to be conducted in a trial to decide whether a person being accused of a murder is guilt or not-guilty? Polygraph test accuracy is a major limitation for the polygraph device.

A study also suggests that the polygraph device is racially discriminating. An innocent black person is more likely to fail a polygraph test (i.e. become 'false positives') than an innocent white person. Moreover, according to data published on the AntiPolygraph website, "only 23.5% of innocent blacks were correctly classified as being non-deceptive" by the polygraph test.

Add to the above information, the facts that -
  • one can easily learn to control the so-called 'symptoms' of lying
  • spies are trained to be able to pass a polygraph test without being detected
  • a polygraph does not (and cannot) measure all 'symptoms' in a lying person
Practiced Liars and Polygraph
Lie Detector Test
Suppose I was to ask you your name as part of the polygraph test. Now suppose I was to tell you to lie the next time I asked you your name, and to say instead that your name is 'Keith/Katherine Rogers'. Now, I give you enough time to practice. I ask you again and again what your name is, what your name is. Each time, you give me your 'false' name. With each time that I ask you your name, you start sounding more and more confident. Now, I ask you to take the polygraph test and ask you your name once again, and you tell me your false name. Would the polygraph device be able to detect the lie? I don't think so; for the simple reason that with a practiced lie, your heart wouldn't race, your palms wouldn't sweat, your pulse wouldn't spike, and it is exactly this that the polygraph measures. Same may be the case with compulsive liars, impulsive liars, habitual liars or pathological liars. Can you still believe the lie detector? Do you still think polygraph tests are accurate?
There are more facts about polygraph tests that go against it rather than stand for it. There isn't, in fact, a foolproof method to tell if someone is lying or not. If there was, there would be no terrorist attacks, no murders, no robberies, no heartaches. However, every liar should remember that there is one person that he/she can never fool, and he/she will see this person every time they look in the mirror. Can you look in the mirror without flinching?