Lie Detection and Interrogation
(Polygraph)
Polygraph - popularly referred to as lie detector. - measures and records several psychological indices such as blood pressure, pulse, respiration and skin conductivity while the subject is asked ans answers a series of questions.
- literally means "many writings". - is derived from two Greek words "Poly"- which means many and "Graphos" which means writing.
Personalities who contributed to the development of the polygraph machine.
Two types of present day polygraph instrumentation
Types of Questions in a Polygraph Test 1. Control Question - preliminary information question 2. Irrelevant Question - 3. Relevant Question - In a polygraph test, the types of questions alternates, the test is passed if the physiological responses during the probable lie control questions are larger than those during the relevant question. Lie Detection - is the practice of determining whether someone is lying.
Three Basic Approaches To The Polygraph Test 1. The Control Question Test (CQT) - this test compares the physiological response to relevant questions about the crime with the response to questions relating to possible prior misdeeds. This test is often used to determine whether certain criminal suspects should be prosecuted or classified as uninvolved in the crime. 2. The Directed Lie Test (DLT) - this test tries to detect lying by comparing physiological responses when the subject is told to deliberately lie to responses when they tell the truth. 3. The Guilty Knowledge Test (GKT) - this test compares physiological responses to multiple choice type questions about the crime, one choice of which contains information only the crime investigators and the criminal would know about. 3 Phases Of A Polygraph Examination 1. Pre-Test Phase - the examiner discusses with the subject the test issue, review the test questions that will be ask during the test and assess the subjects emotional and physiological suitability to undergo the polygraph test. 2. Testing Phase - subjects physiological responses are recorded as the subject answers a set of questions reviewed earlier. 3. Post Test Phase - examiner reviews test data obtained and interprets the polygraph chart. Conclusions That A Polygraph Examiner May Reach 1. Subject is telling the truth 2. Subject is not telling the truth 3. The result is inconclusive * A polygraph test normally lasts between one and a half hours to two and a half hours. * Polygraph test result in the philippines is not admissible in evidence as proof of the guilt of an accused. * Polygraph test is voluntary. * The accuracy of polygraph test is about 90% provided the examiner is competent and the polygraph machine is in good working condition. * Polygraph is an investigative tool. * The principle behind a lie detection test is that when the subject hears a questions which he or she intends to lie, the brain interprets and triggers automatic and uncontrollable physiological changes captured by the polygraph. Who Uses The Polygraph 1. Law Enforcement Agencies 2. Legal Community 3. Private Sector Kinds of Errors in a Polygraph Test 1. False Positive - occurs when a truthful examinee is reported as being deceptive. 2. False Negative - when a deceptive examinee is reported as truthful. Causes of Polygraph Errors 1. Failure of examiner to properly prepare the examinee for the examination. 2. Misreading of the physiological data on the polygraph charts. 3. Defective polygraph machine. Reactions - changes in blood pressure, pulse rate, breathing and sweat activity. Review Questions 1: Next Page |
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