Do Polygraph Tests Work?

How can a polygraph expert confidently claim that someone is lying when there are unreliable factors? Most people who are going through the criminal process will be stressed out, especially during a test which may potentially incriminate them. In order to diminish this possibility for error, the polygraph expert asks a series of questions which are both neutral and stressful before the test begins in order to gauge the physical response of the suspect. This is called an experimental ‘control’. Once the actual test is taken, the expert will be able to compare those results to the ones during the pre-test in order to confirm that the stress response while lying is actually different from the one during a stressful topic. By using this method, the test is said to have around a 80-90% rate of accuracy.

So if the test is this accurate, why can’t it be used as evidence? Unfortunately, even if we are fairly sure that someone is lying about something that does not automatically prove their innocence or guilt. There are still many factors which can lead to incorrect results. If incorrect results were admitted during a trial, the jury might send an innocent person to jail simply based on the fact that they are ‘lying’ about what happened. Polygraphs can have a large impact to the jury’s perception of a case, depending on how they are presented.