A common misconception in forensic science is the reliability of polygraph tests, often featured in crime dramas and high-profile cases, in determining whether someone is lying.

These tests measure physiological responses – such as heart rate, blood pressure, respiration and skin conductivity – while subjects answer a series of questions. The assumption is that deceptive answers will provoke distinct physiological reactions. However, the effectiveness of these tests is widely disputed.

Research shows that polygraphs do not detect lies directly but measure stress, which can arise from various non-deceptive factors, leading to false positives where truthful people are misidentified as liars, or false negatives where deceivers are overlooked.

The American Psychological Association and other expert bodies have questioned the polygraph’s accuracy, estimating its reliability at about 70 per cent, far from infallible. Consequently, many jurisdictions around the world do not accept polygraph results as court evidence, highlighting that the trust in polygraphs as definitive lie detectors is more myth than reality.