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Polygraph examiners use polygraph equipment and techniques to determine whether individuals have answered questions truthfully or dishonestly. Polygraphs, often called "lie detectors," are instruments that measure and record certain nonvoluntary body responses that are affected by the individual's emotional state. To judge whether the subject has answered all the questions truthfully, the examiner compares the reactions recorded for questions that are not likely to cause stress with the reactions recorded for other questions. More than 2,500 polygraph examiners are members of the American Polygraph Association.