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What is the Polygraph / Lie Detector?

A polygraph is a diagnostic instrument used by a formally trained examiner for the purpose of collecting, measuring, and recording selected physiological data obtained from an examinee as he or she answers a series of questions relating to a specific issue — whether criminal, civil, or private — during a polygraph examination. This data will then be analysed and evaluated for psychophysiological credibility assessment.

Polygraph Measurement:
Polygraph test data is a combination of physiological proxies that have been shown to vary significantly in response to different types of test questions as a function of deception and truth telling. Test results are probabilistic descriptions of a margin of uncertainty or level of confidence surrounding a categorical conclusion.

The Theory of Polygraph:
The analytic theory of polygraph testing is that greater changes in physiological activity are loaded at different types of test stimuli as a function of deception and truth telling in response to relevant target stimuli.

The polygraph instrument records data from sensors that monitor autonomic and physical activity, including respiration, cardiovascular, electrodermal and somatic activity, in response to test stimulus questions.

Although lies per se cannot be measured in the same way as a physical substance, several measurable physiological responses have been shown to be statistically correlated with differences in the strength of responses to lies and truth-telling.

To work out results a numerical score is assigned to these responses based on scientific structural model. A categorical result based on the recorded physiological data, indicating either deception or truth-telling, For convenience, the polygraph test is often referred to simplistically as a lie-detector test.

There are 3 phases of a polygraph test: