Lie detector tests, or polygraphs, are not always accurate for several reasons, including:
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Physiological symptoms can be affected by stress or anxiety, which can make a person appear deceitful when they’re not. This is one of the primary reasons why lie detector tests can yield inaccurate results—innocent individuals may experience physiological responses similar to those of someone who is lying simply due to nervousness or anxiety during the testing process.
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Test subjects can manipulate the tests by remaining calm during the test. Some individuals may be skilled at controlling their physiological responses or may simply not feel anxious when lying, leading to misleading results.
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Tests often malfunction, causing records to be recorded inaccurately. While modern polygraphs are generally reliable, there can still be technical issues that might affect the accuracy of the readings.
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Test administrators don’t have a strict enough protocol to ensure data is collected accurately each time a polygraph is conducted. Variations in how different administrators conduct tests can lead to inconsistencies in the results.
All of these factors contribute to the reason that lie detector tests are seen as unreliable and are not universally accepted as valid evidence in legal settings.