In my last blog post I talked about how a person can detect a liar and what type of person is best at it. In this post I want to explore polygraph tests and their accuracy. For those who don’t know, a polygraph test is a machine that records the body movements of a person while the instructor asks them a number of questions. It measures heart rate, blood pressure, and activeness of the person’s sweat glands.

Null Hypothesis: Polygraph test’s  are not accurate lie detectors.

Alternative Hypothesis: Polygraph test’s are accurate lie detectors.

Even though this is a very prevalent and controversial topic, I found it hard to find accurate studies regarding the accuracy polygraphs. Polygraph tests don’t directly detect lies. The instructor draws conclusions from the responses of the body to the “Control Question Technique”. He’ll ask questions about the situation, but he’ll also ask control questions that are completely unrelated to the situation and then analyze the body reactions to each question. If a person is lying, their heart rate will increase or they will perspire more.  However, there are many third variables that can affect the test such as how the examiner asks the questions and how the suspect interprets the questions. Also a person’s anxiety about the test could affect the results.

According to Richard Wiseman, professor of the public understanding of psychology at the University of Hertfordshire, testing the accuracy is difficult,”because you can’t simply ask a criminal whether he was lying or not, the only method would be to use polygraphs in cases where the true answer had already been established using other evidence. Then it would be possible to check the polygraph’s responses against reality in a high-stakes situation.If the examiner was unaware of the true answers, then that would be a proper double-blind scientific study. But there have been very few trials like that.” (Chivers 1). He also says that the test could give false-positives and wrongly accuse innocent people of lying.

Another thing that puts the validity of this test in jeopardy is the ability to cheat on it.  Since the instructor concludes a person is no lying when their stress levels are equal for both the control and crime questions. You can think scary thoughts or inflict physical pain on yourself to increase your heart rate and make yourself sweat. Taking an anti-depressant before the test can also affect the results.

To conclude: I would accept the null hypothesis and reject the alternative hypothesis.