10 of Psychology's Greatest Myths

7 / 11
7 / 11

Lie Detector Tests Are Accurate

Those who operate polygraph -- "Lie Detector" -- tests often boast that they are 99% accurate. The reality is that nobody, not even a machine, can accurately tell when somebody is lying.

Lie detector tests operate under the assumption that telltale physiological signs reveal when people aren't telling the truth. Thus, polygraphs measure indicators like skin conductance, blood pressure, and respiration. When these signs spike out of the test-taker's normal range in response to a question, the operator interprets that a lie has been told.

But such physiological reactions are not universal. Moreover, when one learns to control factors like perspiration and heart rate, one can easily pass a lie detector test.

(Image: Shutterstock)

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