A polygraph does not detect lies directly; it measures physiological responses such as heart rate, breathing, and skin conductivity that tend to rise under stress, on the assumption that lying causes more stress than truth telling. The assumption does not hold for everyone. A person telling the truth but terrified of not being believed can show the same physiological spike as someone actually lying, and a practiced liar who feels little anxiety about deception can pass cleanly. Courts in most jurisdictions do not admit polygraph results as evidence for exactly this reason: the test measures something correlated with lying, not lying itself.
According to the passage, why do most courts not admit polygraph results as evidence?
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Correct answer to question 113 (Paragraph Comprehension): The test measures stress responses correlated with lying, not lying itself
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The final sentence gives the reason directly: the test measures something correlated with lying, not lying itself.
Updated: November 2026
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