Why does nervousness make polygraph results difficult to interpret?

Nervousness makes polygraph results difficult to interpret because the instrument does not measure deception directly; rather, it records physiological responses such as blood pressure, pulse, and perspiration.12

These involuntary reactions are often associated with anxiety or nervous excitement, which are common feelings for anyone undergoing an interrogation. Because the polygraph cannot reliably distinguish between the physiological arousal caused by the act of lying and the arousal caused by simple nervousness or fear, the test's validity is frequently questioned.12

If a subject experiences significant stress, their physiological readings may mimic the patterns expected during deception, even when they are telling the truth. This ambiguity is why polygraph results are often considered unreliable as definitive proof and why their admissibility in judicial proceedings remains limited. It is ethically imperative to recognize these limitations, as relying on flawed interpretations of physiological data risks misjudging an individual's honesty.12